Sometimes, a user may need to dispatch a webhook to an authenticated endpoint.

Django (somewhat sensibly) does not allow inline credentials in URLFields, both

in forms and models, but in this case we want to allow it.
This change makes use of a new backport of Django 1.8's URLValidator, which

supports credentials. The URL is then split and credentials (if included) are

pulled out and added to a HTTPBasicAuthHandler for the url open.

Verified that I was able to save webhook targets that included credentials

  in the URL.
Checked that things that definitely weren't URLs were still rejected.
Ran unit tests.