FEATURE: default notification level for group messages

also fixes it so staff can amend other user's group notification level

db/migrate/20170420163628_add_default_notification_level_to_group.rb

@@ -0,0 +1,11 @@
+class AddDefaultNotificationLevelToGroup < ActiveRecord::Migration
+  def up
+    add_column :groups, :default_notification_level, :integer, default: 3, null: false
+    # don't auto watch 'moderators' it is just way too loud
+    execute 'UPDATE groups SET default_notification_level = 2 WHERE id = 2'
+  end
+
+  def down
+    remove_column :groups, :default_notification_level
+  end
+end