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/signature_sheets_spec.rb

@@ -1,7 +1,6 @@
 require "rails_helper"
 
 describe "Signature sheets" do
-
   before do
     admin = create(:administrator)
     login_as(admin.user)
@@ -73,11 +72,9 @@ describe "Signature sheets" do
 
       expect(page).to have_content "1 support"
     end
-
   end
 
   context "Create throught all required_fields_to_verify of custom census api" do
-
     before do
       Setting["feature.remote_census"] = true
       Setting["remote_census.request.date_of_birth"] = "some.value"
@@ -123,7 +120,6 @@ describe "Signature sheets" do
 
       expect(page).to have_content "1 support"
     end
-
   end
 
   scenario "Errors on create" do
@@ -162,5 +158,4 @@ describe "Signature sheets" do
       expect(page).to have_content 2
     end
   end
-
 end