promotion - remove legacy promotion in the UI

This pull request contains changes to remove the legacy
promotion of products/repos/packages/errata/distributions
from the UI.  After this change, the only content type
that may be promoted is content views.  

There will be additional commits to remove the other 
components of the promotion, including updates to
model, cli/api and migrations (for handling the
current content in the default views).

Also, this pull request is not intended to 're-write' or change
how the basic promotions work; however, it can be anticipated
that it will change in the future.

It should also be noted that there are a few places in 
the code that were highlighed as TODO.  Those are areas
that have nothing to do with the removal of the legacy
promotion and they will be addressed separately.
The key TODOs were: 
1. add support for handling conflicts associated with content views when multiple users are working on a changeset and 
2. add logic so that a user may not promote a content view that is currently being published or refreshed.