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/admin/homepage/homepage_spec.rb

@@ -1,7 +1,6 @@
 require "rails_helper"
 
 describe "Homepage" do
-
   before do
     Setting["homepage.widgets.feeds.proposals"] = false
     Setting["homepage.widgets.feeds.debates"] = false
@@ -20,9 +19,7 @@ describe "Homepage" do
   let(:user)                 { create(:user) }
 
   context "Header" do
-
     scenario "Admin menu links to homepage path" do
-
       visit new_admin_widget_card_path(header_card: true)
 
       click_link Setting["org_name"] + " Administration"
@@ -32,7 +29,6 @@ describe "Homepage" do
   end
 
   context "Feeds" do
-
     scenario "Proposals", :js do
       5.times { create(:proposal) }
 
@@ -120,7 +116,6 @@ describe "Homepage" do
     end
 
     xscenario "Deactivate"
-
   end
 
   scenario "Cards" do
@@ -175,5 +170,4 @@ describe "Homepage" do
 
     expect(page).to have_content("Recommendations that may interest you")
   end
-
 end