Engine: Initial work to allow Katello to be loaded as a Rails engine
alongside Foreman and be able to access the Foreman application.

Note, this does not enable any UI/API capabilities, the scope of this
initial commit is to get Katello's dependencies loaded and Foreman
running with Katello as an engine mounted.
Engine: Namespacing controllers.
Engine: Namespacing helpers.
Engine: Namespacing mailers.
Engine: Namespacing models.
Engine: Namespacing app/lib.
Engine: Namespacing views.
Engine: Namespacing assets.
Engine: Cleaning up lib.
Engine: Adding namespace pathing to stylesheet imports.
Merge pull request #3170 from ehelms/engine-namespace

Engine namespace
Engine: Namespacing controllers.
Engine: Namespacing helpers.
Engine: Namespacing mailers.
Engine: Namespacing models.
Engine: Namespacing app/lib.
Engine: Namespacing views.
Engine: Namespacing assets.
Engine: Cleaning up lib.
Engine: Adding namespace pathing to stylesheet imports.