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/shared/features/relationable.rb

@@ -1,5 +1,4 @@
 shared_examples "relationable" do |relationable_model_name|
-
   let(:relationable) { create(relationable_model_name.name.parameterize(separator: "_").to_sym) }
   let(:related1) { create([:proposal, :debate, :budget_investment].sample) }
   let(:related2) { create([:proposal, :debate, :budget_investment].sample) }
@@ -99,7 +98,6 @@ shared_examples "relationable" do |relationable_model_name|
 
     expect(related_content.related_content_scores.find_by(user_id: user.id, related_content_id: related_content.id).value).to eq(1)
     expect(related_content.opposite_related_content.related_content_scores.find_by(user_id: user.id, related_content_id: related_content.opposite_related_content.id).value).to eq(1)
-
   end
 
   scenario "related content can be scored negatively", :js do