Inherit from ActiveAdmin::ApplicationController, instead of Main App ApplicationController

This allows users to use active_admin without worrying about what's in their existing application_controller.rb. This allows the front end and the back end to remain segregated. This also solves a problem with cancan interfering with admin resources if you don't want it to.

This can also be overridden in the main app by creating an controllers/acitve_admin/application_controller.rb.