Add and apply EmptyLineAfterGuardClause rule

We were inconsistent on this one. I consider it particularly useful when
a method starts with a `return` statement.

In other cases, we probably shouldn't have a guard rule in the middle of
a method in any case, but that's a different refactoring.

app/controllers/legislation/processes_controller.rb

@@ -159,6 +159,7 @@ class Legislation::ProcessesController < Legislation::BaseController
 
     def set_process
       return if member_method?
+
       @process = ::Legislation::Process.find(params[:process_id])
     end
 end