Account - External Authentication [MJ-252]

Adds a view that allows for authentication of My.jobs accounts by third parties.

Expects a query parameter of "callback" containing the url to be redirected to after successful authorization.
The HTTP_REFERER header is required. This header and the callback must share the same domain (a request originating from jobs.jobs can't ask us to redirect to indiana.jobs, for example).

The requirement for HTTP_REFERER means checking this out in a browser is a very manual process. I've managed it by just navigating to `google.com`, opening a javascript console, and entering `window.location = 'http://localhost:8000/authorize?callback=https://www.google.com`

There are probably issues, but it's ready for more eyes to examine.

All tests pass.