Engine: updates to devel branch enhancements to support engine

There have been several enhancements that have gone in to
the devel branch.  This commit contains changes that have
been identified (so far) that are needed to enable them
to work with katello as an engine.

This includes changes such as:
- minor updates for pathing (e.g katello/)
- minor updates for rails path helpers (e.g. _katello_)
- renaming 'menu' to 'main_menu'.  This is unfortunately
  necessary, since foreman has already defined 'menu' and
  the helper is being loaded as a module on top of foreman.