Adding a little bit to the django auth part of mongoengine

[MRigal]

Gosh I didn't realize at the beginning how deep the hole is !!! But maybe this small additions may show to other people what is working and what not, and how much is missing here.

It's a kind of "documenting via testing" purpose.

This allowed to not loose the aborted PR #756 and actually gave me some inside on the opportunity to really detach the django part, as proposed in issue #958

If you think it helps nothing to merge it in, I'll be fine with it.

[landscape-bot]

Repository health increased by 0.05% when pulling a9bd3c5 on MRigal:django-auth-permissions into 19dc312 on MongoEngine:master.

• No new problems were introduced.
• 2 problems were fixed (including 0 errors and 2 code smells).

[coveralls]

Coverage increased (+0.0%) to 73.03% when pulling a9bd3c5 on MRigal:django-auth-permissions into 19dc312 on MongoEngine:master.

[landscape-bot]

Repository health increased by 0.05% when pulling 82cc4bd on MRigal:django-auth-permissions into 19dc312 on MongoEngine:master.

• No new problems were introduced.
• 2 problems were fixed (including 0 errors and 2 code smells).

[coveralls]

Coverage increased (+0.0%) to 73.03% when pulling 82cc4bd on MRigal:django-auth-permissions into 19dc312 on MongoEngine:master.

[landscape-bot]

Repository health increased by 0.05% when pulling 74e4d52 on MRigal:django-auth-permissions into 19dc312 on MongoEngine:master.

• No new problems were introduced.
• 2 problems were fixed (including 0 errors and 2 code smells).

[coveralls]

Coverage increased (+0.0%) to 73.03% when pulling 74e4d52 on MRigal:django-auth-permissions into 19dc312 on MongoEngine:master.

[mmellison]

Label and close as part of Django split. See #973.