Use the Rails cache in the railtie

The app that is yielded in the railtie doesn't have a cache method.
Instead, get the cache from Rails directly.
Load the railtie after the Cached module

Loading the railtie before the ActiveRemote::Cached module doesn't fire
the ActiveSupport::Concern hooks, which means none of the class methods
are extended.

Loading the railtie after the module is interpreted fixes the problem.