Use a button for non-GET table actions

Links acting like buttons have a few disadvantages.

First, screen readers will announce them as "links". Screen reader users
usually associate links with "things that get you somewhere" and buttons
with "things that perform an action". So when something like "Delete,
link" is announced, they'll probably think this is a link which will
take them to another page where they can delete a record.

Furthermore, the URL of the link for the "destroy" action might be the
same as the URL for the "show" action (only one is accessed with a
DELETE request and the other one with a GET request). That means screen
readers could announce the link like "Delete, visited link", which is
very confusing.

They also won't work when opening links in a new tab, since opening
links in a new tab always results in a GET request to the URL the link
points to.

Finally, submit buttons work without JavaScript enabled, so they'll work
even if the JavaScript in the page hasn't loaded (for whatever reason).

For all these reasons (and probably many more), using a button to send
forms is IMHO superior to using links.

There's one disadvantage, though. Using `button_to` we create a <form>
tag, which means we'll generate invalid HTML if the table is inside
another form. If we run into this issue, we need to use `button_tag`
with a `form` attribute and then generate a form somewhere else inside
the HTML (with `content_for`).

Note we're using `button_to` with a block so it generates a <button>
tag. Using it in a different way the text would result in an <input />
tag, and input elements can't have pseudocontent added via CSS.

The following code could be a starting point to use the `button_tag`
with a `form` attribute. One advantage of this approach is screen
readers wouldn't announce "leaving form" while navigating through these
buttons. However, it doesn't work in Internet Explorer.

```
ERB:

<% content_for(:hidden_content, form_tag(path, form_options) {}) %>
<%= button_tag text, button_options %>

Ruby:

def form_id
  path.gsub("/", "_")
end

def form_options
  { id: form_id, method: options[:method] }
end

def button_options
  html_options.except(:method).merge(form: form_id)
end

Layout:

<%= content_for :hidden_content %> # Right before the `</body>`
```

spec/system/admin/poll/booth_assigments_spec.rb

@@ -61,11 +61,11 @@ describe "Admin booths assignments", :admin do
         expect(page).to have_content(booth.name)
         expect(page).to have_content "Unassigned"
 
-        click_link "Assign booth"
+        click_button "Assign booth"
 
         expect(page).not_to have_content "Unassigned"
         expect(page).to have_content "Assigned"
-        expect(page).to have_link "Unassign booth"
+        expect(page).to have_button "Unassign booth"
       end
 
       visit admin_poll_path(poll)
@@ -100,11 +100,11 @@ describe "Admin booths assignments", :admin do
         expect(page).to have_content(booth.name)
         expect(page).to have_content "Assigned"
 
-        click_link "Unassign booth"
+        click_button "Unassign booth"
 
         expect(page).to have_content "Unassigned"
         expect(page).not_to have_content "Assigned"
-        expect(page).to have_link "Assign booth"
+        expect(page).to have_button "Assign booth"
       end
 
       visit admin_poll_path(poll)
@@ -127,11 +127,11 @@ describe "Admin booths assignments", :admin do
         expect(page).to have_content(booth.name)
         expect(page).to have_content "Assigned"
 
-        accept_confirm { click_link "Unassign booth" }
+        accept_confirm { click_button "Unassign booth" }
 
         expect(page).to have_content "Unassigned"
         expect(page).not_to have_content "Assigned"
-        expect(page).to have_link "Assign booth"
+        expect(page).to have_button "Assign booth"
       end
     end
 
@@ -143,8 +143,7 @@ describe "Admin booths assignments", :admin do
       within("#poll_booth_#{booth.id}") do
         expect(page).to have_content(booth.name)
         expect(page).to have_content "Assigned"
-
-        expect(page).not_to have_link "Unassign booth"
+        expect(page).not_to have_button "Unassign booth"
       end
     end
   end

spec/system/admin/poll/officers_spec.rb

@@ -19,14 +19,16 @@ describe "Admin poll officers", :admin do
     click_button "Search"
 
     expect(page).to have_content user.name
-    click_link "Add"
+
+    click_button "Add"
+
     within("#officers") do
       expect(page).to have_content user.name
     end
   end
 
   scenario "Delete" do
-    accept_confirm { click_link "Delete position" }
+    accept_confirm { click_button "Delete position" }
 
     expect(page).not_to have_css "#officers"
   end

spec/system/admin/poll/polls_spec.rb

@@ -119,7 +119,7 @@ describe "Admin polls", :admin do
       visit admin_polls_path
 
       within("#poll_#{poll.id}") do
-        accept_confirm { click_link "Delete" }
+        accept_confirm { click_button "Delete" }
       end
 
       expect(page).to have_content("Poll deleted successfully")
@@ -133,7 +133,7 @@ describe "Admin polls", :admin do
       visit admin_polls_path
 
       within(".poll", text: "Do you support CONSUL?") do
-        accept_confirm { click_link "Delete" }
+        accept_confirm { click_button "Delete" }
       end
 
       expect(page).to     have_content("Poll deleted successfully")
@@ -150,7 +150,7 @@ describe "Admin polls", :admin do
       visit admin_polls_path
 
       within(".poll", text: "Do you support CONSUL?") do
-        accept_confirm { click_link "Delete" }
+        accept_confirm { click_button "Delete" }
       end
 
       expect(page).to have_content "Poll deleted successfully"
@@ -164,7 +164,7 @@ describe "Admin polls", :admin do
       visit admin_polls_path
 
       within("#poll_#{poll.id}") do
-        accept_confirm { click_link "Delete" }
+        accept_confirm { click_button "Delete" }
       end
 
       expect(page).to have_content("You cannot delete a poll that has votes")

spec/system/admin/poll/questions/answers/documents/documents_spec.rb

@@ -28,7 +28,7 @@ describe "Documents", :admin do
     visit admin_answer_documents_path(answer)
     expect(page).to have_content(document.title)
 
-    accept_confirm { click_link "Delete" }
+    accept_confirm { click_button "Delete" }
 
     expect(page).not_to have_content(document.title)
   end

spec/system/admin/poll/questions_spec.rb

@@ -17,7 +17,7 @@ describe "Admin poll questions", :admin do
       expect(page).to have_content(question1.title)
       expect(page).to have_link "Edit answers"
       expect(page).to have_link "Edit"
-      expect(page).to have_link "Delete"
+      expect(page).to have_button "Delete"
     end
 
     visit admin_poll_path(poll2)
@@ -27,7 +27,7 @@ describe "Admin poll questions", :admin do
       expect(page).to have_content question2.title
       expect(page).to have_link "Edit answers"
       expect(page).to have_link "Edit"
-      expect(page).to have_link "Delete"
+      expect(page).to have_button "Delete"
     end
 
     visit admin_poll_path(poll3)
@@ -38,7 +38,7 @@ describe "Admin poll questions", :admin do
       expect(page).to have_link "(See proposal)", href: proposal_path(question3.proposal)
       expect(page).to have_link "Edit answers"
       expect(page).to have_link "Edit"
-      expect(page).to have_link "Delete"
+      expect(page).to have_button "Delete"
     end
   end
 
@@ -142,7 +142,7 @@ describe "Admin poll questions", :admin do
     visit admin_poll_path(poll)
 
     within("#poll_question_#{question1.id}") do
-      accept_confirm { click_link "Delete" }
+      accept_confirm { click_button "Delete" }
     end
 
     expect(page).not_to have_content(question1.title)

spec/system/admin/poll/shifts_spec.rb

@@ -174,7 +174,7 @@ describe "Admin shifts", :admin do
 
     expect(page).to have_css(".shift", count: 1)
     within("#shift_#{shift.id}") do
-      accept_confirm { click_link "Remove" }
+      accept_confirm { click_button "Remove" }
     end
 
     expect(page).to have_content "Shift removed"
@@ -198,7 +198,7 @@ describe "Admin shifts", :admin do
 
     expect(page).to have_css(".shift", count: 1)
     within("#shift_#{shift.id}") do
-      accept_confirm { click_link "Remove" }
+      accept_confirm { click_button "Remove" }
     end
 
     expect(page).not_to have_content "Shift removed"
@@ -225,7 +225,7 @@ describe "Admin shifts", :admin do
 
     expect(page).to have_css(".shift", count: 1)
     within("#shift_#{shift.id}") do
-      accept_confirm { click_link "Remove" }
+      accept_confirm { click_button "Remove" }
     end
 
     expect(page).not_to have_content "Shift removed"