Use a custom url for proposal polls

Before we used the standard poll url (vota/:id) for a user generated poll.

However this url is considered too important for this kind of polls, so we are changing it to a namespaced url (proposals/:proposal_id/polls/:id)

spec/features/dashboard/polls_spec.rb

@@ -206,6 +206,7 @@ feature "Polls" do
       expect(page).to have_content(I18n.l(poll.starts_at.to_date))
       expect(page).to have_content(I18n.l(poll.ends_at.to_date))
       expect(page).to have_link(poll.title)
+      expect(page).to have_link(poll.title, href: proposal_poll_path(proposal, poll))
     end
   end
 end