Simplify tests checking dates are present

When we create a record like a debate or an event and we check the page
content, we want to make sure that today's date is present, since it's
the date where the record is supposed to have been created.

This way we avoid querying the database after the browser has been
started.

spec/system/admin/stats_spec.rb

@@ -216,7 +216,7 @@ describe "Stats", :admin do
   end
 
   context "graphs" do
-    scenario "event graphs" do
+    scenario "event graphs", :with_frozen_time do
       campaign = create(:campaign)
 
       visit root_path(track_id: campaign.track_id)
@@ -227,9 +227,9 @@ describe "Stats", :admin do
       end
 
       expect(page).to have_content "#{campaign.name} (1)"
+
       within("#graph") do
-        event_created_at = Ahoy::Event.find_by(name: campaign.name).time
-        expect(page).to have_content event_created_at.strftime("%Y-%m-%d")
+        expect(page).to have_content Date.current.strftime("%Y-%m-%d")
       end
     end
   end

spec/system/debates_spec.rb

@@ -201,7 +201,7 @@ describe "Debates" do
     expect(page).to have_content("-6 votes")
   end
 
-  scenario "Create" do
+  scenario "Create", :with_frozen_time do
     author = create(:user)
     login_as(author)
 
@@ -216,7 +216,7 @@ describe "Debates" do
     expect(page).to have_content "Debate created successfully."
     expect(page).to have_content "This is very important because..."
     expect(page).to have_content author.name
-    expect(page).to have_content I18n.l(Debate.last.created_at.to_date)
+    expect(page).to have_content I18n.l(Date.current)
   end
 
   scenario "Create with invisible_captcha honeypot field", :no_js do

spec/system/management/proposals_spec.rb

@@ -4,7 +4,7 @@ describe "Proposals" do
   let(:user) { create(:user, :level_two) }
 
   context "Create" do
-    scenario "Creating proposals on behalf of someone" do
+    scenario "Creating proposals on behalf of someone", :with_frozen_time do
       login_managed_user(user)
       login_as_manager
       click_link "Create proposal"
@@ -31,7 +31,7 @@ describe "Proposals" do
       expect(page).to have_content "This is very important because..."
       expect(page).to have_content "https://www.youtube.com/watch?v=yRYFKcMa_Ek"
       expect(page).to have_content user.name
-      expect(page).to have_content I18n.l(Proposal.last.created_at.to_date)
+      expect(page).to have_content I18n.l(Date.current)
 
       expect(page).to have_current_path(management_proposal_path(Proposal.last))
     end

spec/system/proposals_spec.rb

@@ -355,7 +355,7 @@ describe "Proposals" do
     expect(page).to have_css "meta[property='og:title'][content=\'#{proposal.title}\']", visible: :hidden
   end
 
-  scenario "Create and publish" do
+  scenario "Create and publish", :with_frozen_time do
     author = create(:user)
     login_as(author)
 
@@ -387,7 +387,7 @@ describe "Proposals" do
     expect(page).to have_content author.name
     expect(page).to have_content "Refugees"
     expect(page).to have_content "Solidarity"
-    expect(page).to have_content I18n.l(Proposal.last.created_at.to_date)
+    expect(page).to have_content I18n.l(Date.current)
   end
 
   scenario "Create with invisible_captcha honeypot field", :no_js do