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/proposals_controller.rb

@@ -151,6 +151,7 @@ class ProposalsController < ApplicationController
 
     def load_featured
       return unless !@advanced_search_terms && @search_terms.blank? && @tag_filter.blank? && params[:retired].blank? && @current_order != "recommendations"
+
       if Setting["feature.featured_proposals"]
         @featured_proposals = Proposal.not_archived.unsuccessful
                               .sort_by_confidence_score.limit(Setting["featured_proposals_number"])