Use buttons for budgets actions

Using buttons for non-GET actions is better for accessibility, as
mentioned in commit 5311daadf.

spec/system/admin/budget_investments_spec.rb

@@ -496,11 +496,11 @@ describe "Admin budget investments", :admin do
       check "Winners"
       click_button "Filter"
 
-      expect(page).to have_link "Calculate Winner Investments"
+      expect(page).to have_button "Calculate Winner Investments"
 
       visit edit_admin_budget_path(budget)
 
-      expect(page).to have_link "Calculate Winner Investments"
+      expect(page).to have_button "Calculate Winner Investments"
 
       select "Accepting projects", from: "Active phase"
       click_button "Update Budget"
@@ -513,14 +513,14 @@ describe "Admin budget investments", :admin do
       check "Winners"
       click_button "Filter"
 
-      expect(page).not_to have_link "Calculate Winner Investments"
+      expect(page).not_to have_button "Calculate Winner Investments"
       expect(page).to have_content 'The budget has to stay on phase "Balloting projects", '\
                                    '"Reviewing Ballots" or "Finished budget" in order '\
                                    "to calculate winners projects"
 
       visit edit_admin_budget_path(budget)
 
-      expect(page).not_to have_link "Calculate Winner Investments"
+      expect(page).not_to have_button "Calculate Winner Investments"
     end
 
     scenario "Filtering by minimum number of votes" do

spec/system/admin/budgets_spec.rb

@@ -124,11 +124,11 @@ describe "Admin budgets", :admin do
     scenario "Can preview a budget after it is published" do
       visit edit_admin_budget_path(budget)
 
-      accept_confirm { click_link "Publish budget" }
+      accept_confirm { click_button "Publish budget" }
 
       expect(page).to have_content "Participatory budget published successfully"
       expect(page).not_to have_content "This participatory budget is in draft mode"
-      expect(page).not_to have_link "Publish budget"
+      expect(page).not_to have_button "Publish budget"
 
       within_window(window_opened_by { click_link "Preview" }) do
         expect(page).to have_current_path budget_path(budget)
@@ -142,7 +142,7 @@ describe "Admin budgets", :admin do
 
     scenario "Destroy a budget without investments" do
       visit edit_admin_budget_path(budget)
-      click_link "Delete budget"
+      click_button "Delete budget"
 
       expect(page).to have_content("Budget deleted successfully")
       expect(page).to have_content("There are no budgets.")
@@ -153,7 +153,7 @@ describe "Admin budgets", :admin do
       budget.valuators << create(:valuator)
 
       visit edit_admin_budget_path(budget)
-      click_link "Delete budget"
+      click_button "Delete budget"
 
       expect(page).to have_content "Budget deleted successfully"
       expect(page).to have_content "There are no budgets."
@@ -163,7 +163,7 @@ describe "Admin budgets", :admin do
       create(:budget_investment, heading: heading)
 
       visit edit_admin_budget_path(budget)
-      click_link "Delete budget"
+      click_button "Delete budget"
 
       expect(page).to have_content("You cannot delete a budget that has associated investments")
       expect(page).to have_content("There is 1 budget")
@@ -173,7 +173,7 @@ describe "Admin budgets", :admin do
       create(:poll, budget: budget)
 
       visit edit_admin_budget_path(budget)
-      click_link "Delete budget"
+      click_button "Delete budget"
 
       expect(page).to have_content("You cannot delete a budget that has an associated poll")
       expect(page).to have_content("There is 1 budget")
@@ -335,7 +335,9 @@ describe "Admin budgets", :admin do
 
       visit edit_admin_budget_path(budget)
       expect(page).not_to have_content "See results"
-      click_link "Calculate Winner Investments"
+
+      click_button "Calculate Winner Investments"
+
       expect(page).to have_content "Winners being calculated, it may take a minute."
       expect(page).to have_content winner.title
       expect(page).not_to have_content unselected.title

spec/system/admin/budgets_wizard/budgets_spec.rb

@@ -92,7 +92,7 @@ describe "Budgets wizard, first step", :admin do
 
       expect(page).to have_content "This participatory budget is in draft mode"
       expect(page).to have_link "Preview"
-      expect(page).to have_link "Publish budget"
+      expect(page).to have_button "Publish budget"
     end
   end