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/helpers/admin/proposal_dashboard_actions_helper.rb

@@ -1,6 +1,7 @@
 module Admin::ProposalDashboardActionsHelper
   def active_human_readable(active)
     return t("admin.dashboard.actions.index.active") if active
+
     t("admin.dashboard.actions.index.inactive")
   end