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/features/localization_spec.rb

@@ -1,7 +1,6 @@
 require "rails_helper"
 
 describe "Localization" do
-
   scenario "Wrong locale" do
     I18n.with_locale(:es) do
       create(:widget_card, title: "Bienvenido a CONSUL",
@@ -57,7 +56,6 @@ describe "Localization" do
   end
 
   context "Missing language names" do
-
     let!(:default_enforce) { I18n.enforce_available_locales }
     let!(:default_locales) { I18n.available_locales.dup }
 
@@ -80,6 +78,5 @@ describe "Localization" do
         expect(page).to have_content "wl"
       end
     end
-
   end
 end