specs: migrate from features to system specs

System specs have been available since Rails 5.1, and are better
integrated with the Rails framework.

- Rename `spec/features` to `spec/system`
- Rename `feature do` to `describe do`
- Configure Capybara for system specs

Steps mostly taken from https://medium.com/table-xi/a-quick-guide-to-rails-system-tests-in-rspec-b6e9e8a8b5f6

spec/system/help_spec.rb

@@ -0,0 +1,100 @@
+describe 'Getting help:' do
+  scenario 'a Help button is visible on public pages' do
+    visit '/'
+    within('.new-header') do
+      expect(page).to have_help_button
+    end
+  end
+
+  context 'on pages related to a procedure' do
+    let(:procedure) { create(:procedure, :published, :with_service) }
+
+    scenario 'a Help menu provides administration contacts and a link to the FAQ' do
+      visit commencer_path(path: procedure.path)
+
+      within('.new-header') do
+        expect(page).to have_help_menu
+      end
+
+      within('.help-dropdown') do
+        expect(page).to have_content(procedure.service.email)
+        expect(page).to have_content(procedure.service.telephone)
+        expect(page).to have_link(nil, href: FAQ_URL)
+      end
+    end
+  end
+
+  context 'as a signed-in user' do
+    let(:user) { create(:user) }
+    let(:procedure) { create(:procedure, :with_service) }
+
+    before do
+      login_as user, scope: :user
+    end
+
+    scenario 'a Help button is visible on signed-in pages' do
+      visit dossiers_path
+      within('.new-header') do
+        expect(page).to have_help_button
+      end
+    end
+
+    context 'on a page related to a draft dossier' do
+      let(:dossier) { create(:dossier, user: user, procedure: procedure) }
+
+      scenario 'a Help menu provides administration contacts and a link to the FAQ' do
+        visit dossier_path(dossier)
+
+        within('.new-header') do
+          expect(page).to have_help_menu
+        end
+
+        within('.help-dropdown') do
+          expect(page).to have_content(dossier.procedure.service.email)
+          expect(page).to have_content(dossier.procedure.service.telephone)
+          expect(page).to have_link(nil, href: FAQ_URL)
+        end
+      end
+    end
+
+    context 'on a page related to a submitted dossier' do
+      let(:dossier) { create(:dossier, :en_construction, user: user, procedure: procedure) }
+
+      scenario 'a Help menu provides links to the Messagerie and to the FAQ' do
+        visit dossier_path(dossier)
+
+        within('.new-header') do
+          expect(page).to have_help_menu
+        end
+
+        within('.help-dropdown') do
+          expect(page).to have_link(nil, href: messagerie_dossier_path(dossier))
+          expect(page).to have_link(nil, href: FAQ_URL)
+        end
+      end
+    end
+  end
+
+  context 'as a instructeur' do
+    let(:instructeur) { create(:instructeur) }
+
+    before do
+      login_as instructeur.user, scope: :user
+    end
+
+    scenario 'a Help menu is visible on signed-in pages' do
+      visit instructeur_procedures_path
+      within('.new-header') do
+        expect(page).to have_help_menu
+      end
+    end
+  end
+
+  def have_help_button
+    have_link('Aide', href: FAQ_URL)
+  end
+
+  def have_help_menu
+    have_selector('.help-dropdown')
+  end
+end