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
Allowing oauth secret and key to be set per install and setting the
logger properly. Rest calls to Pulp will now show up in the development
log.