User.get_username() rather than User.name to support custom User models

[acordiner]

This adds support for custom User models which do not contain a username field: https://docs.djangoproject.com/en/1.10/ref/contrib/auth/#django.contrib.auth.models.User.get_username

[coveralls]

Coverage remained the same at 100.0% when pulling bf67430 on acordiner:master into fb323b8 on TracyWebTech:master.

[coveralls]

Coverage remained the same at 100.0% when pulling bf67430 on acordiner:master into fb323b8 on TracyWebTech:master.

[coveralls]

Coverage remained the same at 100.0% when pulling bf67430 on acordiner:master into fb323b8 on TracyWebTech:master.

[coveralls]

Coverage remained the same at 100.0% when pulling bf67430 on acordiner:master into fb323b8 on TracyWebTech:master.

[coveralls]

Coverage remained the same at 100.0% when pulling bf67430 on acordiner:master into fb323b8 on TracyWebTech:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 0cf0938 on acordiner:master into fb323b8 on TracyWebTech:master.

[acordiner]

Any chance to get this merged?

[rougeth]

tks @acordiner :)