Description of problem:
Improve the error checking on content repositories. For example, if you synchronize a custom content provider that has some package group information, but it is somewhat broken then this brokeness makes its way into the User Interface.

When you click on Content Management > Promotions > Library Content > System Templates > %template_name%, Package Groups aren't showing up.  Also, distributions not showing up.

If pulp/grinder/katello could verify package groups do or do not exist and then display them in the UI only if they work correctly it would be ideal.