FEATURE: proper mailing list mode

once enable_mailing_list_mode is enabled any user can elect
to get every post via email unless they opt out of category or topic

db/migrate/20140206215029_add_mailing_list_mode_to_users.rb

@@ -0,0 +1,5 @@
+class AddMailingListModeToUsers < ActiveRecord::Migration
+  def change
+    rename_column :users, :watch_new_topics, :mailing_list_mode
+  end
+end