added missing placeholder method, currently breaks editing a repo
Add supports for pulp notification callbacks

* adds /api/repositories/events POST action
* adds PulpEventHandler class to parse and act on the events.
* adds an option to auto register events on pulp, this however is dead code
at the moment since i would assume the workflow will change once we have
multi-pulp support

to register notifications (in the meanwhile) manually on your pulp
server execute:
pulp-admin event listener http create
added medium uri from pulp repository to os.
Added kickstart content type to repository.
moved the os kickstart and yum repo code Redhat os family class.
repos as hash for the kickstart template.
added support for noarch to the repository scope