Add and apply rubocop rules for empty lines

We were very inconsistent regarding these rules.

Personally I prefer no empty lines around blocks, clases, etc... as
recommended by the Ruby style guide [1], and they're the default values
in rubocop, so those are the settings I'm applying.

The exception is the `private` access modifier, since we were leaving
empty lines around it most of the time. That's the default rubocop rule
as well. Personally I don't have a strong preference about this one.


[1] https://rubystyle.guide/#empty-lines-around-bodies

spec/controllers/concerns/has_filters_spec.rb

@@ -1,7 +1,6 @@
 require "rails_helper"
 
 describe HasFilters do
-
   class FakeController < ActionController::Base; end
 
   controller(FakeController) do

spec/controllers/concerns/has_orders_spec.rb

@@ -1,7 +1,6 @@
 require "rails_helper"
 
 describe HasOrders do
-
   class FakeController < ActionController::Base; end
 
   controller(FakeController) do

spec/controllers/concerns/remotely_translatable_spec.rb

@@ -2,15 +2,12 @@ require "rails_helper"
 include RemotelyTranslatable
 
 describe RemotelyTranslatable do
-
   before do
     Setting["feature.remote_translations"] = true
   end
 
   describe "#detect_remote_translations" do
-
     describe "Should detect remote_translations" do
-
       it "When collections and featured_proposals are not defined in current locale" do
         proposals = create_list(:proposal, 3)
         featured_proposals = create_featured_proposals
@@ -49,7 +46,6 @@ describe RemotelyTranslatable do
           expect(detect_remote_translations(widget_feeds).count).to eq 9
         end
       end
-
     end
 
     it "When defined in current locale should not detect remote_translations" do