Engine: removing user model

The user model previously used by katello was moved to
a user_extensions module, which will be used to extend
the base User that is in the root namespace (::User).
Engine: content views: initial ui/model changes to support engine

This commit has the basic changes to support CRUD actions
in the UI for:
- content view definition
- content view
- filter
- filter rule

There are a few things that still need to be addressed:
- filter rules do not fully work due to issues with 'HashWithIndifferentAccess'
- need to fix a few 404 on loading assets (e.g. font, spinner)
Engine: fix typo in home_helper_patch
Engine: minor changes for User/Org since using app's models
Engine: modifications to support delayed jobs and view publish/refresh

This commit contains several changes to allow support running
delayed jobs (e.g. rake jobs:work from host app) and
publish/refresh of content views.
Merge pull request #2712 from ehelms/enginify

Engine: Adding customized Taxonomix to handle the case of associating
Engine: Removing validation on organization belongs_to.
Engine: reverting the removal of UserModel threadsession

This commit is reverting the change that removed the
UserModel from threadsession.  This was need to
support setting the pulp config.  We plan to revisit this
to find a better alternative.
Engine: content views: updates support org or all-org context

This commit has a few changes to support the fact that
a user may be logged in either within an org or without
an org.
Engine: Updates to pathing for API routes and user notice references.
Engine: Adding Foreman architecture to the repository object.
Engine: extend Host to include a content view
Engine: Clean-up of paths and references in the namespace, updating to Runcible
0.4.12 which requires Pulp 2.2.
Engine: Updates to pathing to support pulling the mediapath from
the first repository added to a Content View.