Add moderator role and add pundit policies for admin actions (#5635)

* Add moderator role and add pundit policies for admin actions

* Add rake task for turning user into mod and revoking it again

* Fix handling of unauthorized exception

* Deliver new report e-mails to staff, not just admins

* Add promote/demote to admin UI, hide some actions conditionally

* Fix unused i18n

db/migrate/20171109012327_add_moderator_to_accounts.rb

@@ -0,0 +1,15 @@
+require Rails.root.join('lib', 'mastodon', 'migration_helpers')
+
+class AddModeratorToAccounts < ActiveRecord::Migration[5.1]
+  include Mastodon::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  def up
+    safety_assured { add_column_with_default :users, :moderator, :bool, default: false }
+  end
+
+  def down
+    remove_column :users, :moderator
+  end
+end