Extract link text to a helper

This way we can use the same code in custom views which won't use the
same text.

app/helpers/legislation_helper.rb

@@ -6,4 +6,8 @@ module LegislationHelper
   def format_date_for_calendar_form(date)
     l(date, format: "%d/%m/%Y") if date
   end
+
+  def new_legislation_proposal_link_text(process)
+    t("proposals.index.start_proposal")
+  end
 end

app/views/legislation/processes/proposals.html.erb

@@ -22,7 +22,10 @@
 
       <div class="small-12 medium-3 column">
         <% if @process.proposals_phase.open? %>
-          <p><%= link_to t("proposals.index.start_proposal"), new_legislation_process_proposal_path(@process), class: 'button expanded' %></p>
+          <p><%= link_to new_legislation_proposal_link_text(@process),
+                         new_legislation_process_proposal_path(@process),
+                         class: 'button expanded',
+                         id: 'create-new-proposal' %></p>
         <% end %>
         <%= render 'legislation/proposals/categories', taggable: @process %>
       </div>