Use describe on feature tests

The `type: :feature` is automatically detected by RSpec because these
tests are inside the `spec/features` folder. Using `feature` re-adds a
`type: :feature` to these files, which will result in a conflict when we
upgrade to Rails 5.1's system tests.

Because of this change, we also need to change `background` to `before`
or else these tests will fail.

spec/features/account_spec.rb

@@ -1,8 +1,8 @@
 require "rails_helper"
 
-feature "Account" do
+describe "Account" do
 
-  background do
+  before do
     @user = create(:user, username: "Manuela Colau")
     login_as(@user)
   end
@@ -177,7 +177,7 @@ feature "Account" do
 
   context "Recommendations" do
 
-    background do
+    before do
       Setting["feature.user.recommendations"] = true
       Setting["feature.user.recommendations_on_debates"] = true
       Setting["feature.user.recommendations_on_proposals"] = true