Suppression list improvements (#867)

config/cron.rb

@@ -26,6 +26,7 @@ module Clockwork
 
   every 1.day, 'every-day', :at => ['03:00'] do
     ProcessMessageRetentionJob.queue(:main)
+    PruneSuppressionListsJob.queue(:main)
   end
 
 end

config/postal.defaults.yml

@@ -13,6 +13,7 @@ general:
   exception_url:
   maximum_delivery_attempts: 18
   maximum_hold_expiry_days: 7
+  suppression_list_removal_delay: 30
   use_local_ns_for_domains: false
 
 web_server: