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/home_spec.rb

@@ -1,9 +1,7 @@
 require "rails_helper"
 
 describe "Home" do
-
   context "For not logged users" do
-
     scenario "Welcome message" do
       visit root_path
 
@@ -17,13 +15,10 @@ describe "Home" do
 
       expect(page).not_to have_content "Recommendations that may interest you"
     end
-
   end
 
   context "For signed in users" do
-
     describe "Recommended" do
-
       before do
         proposal = create(:proposal, tag_list: "Sport")
         user = create(:user, followables: [proposal])
@@ -108,7 +103,6 @@ describe "Home" do
         expect(page).not_to have_content "Recommendations that may interest you"
       end
     end
-
   end
 
   describe "IE alert" do