Initial support to Group and Permission. The /admin can't be exec login in MongoDB yet. Only SQLsDB (SQLite,...)

This code work with django-mongoadmin pluggin.
Adding, adjust and transplant more methods to auth.User model
exposing mongoengine.django module
Merge branch 'add_group_permission' of https://github.com/multmeio/mongoengine into 0.8

Conflicts:
	mongoengine/django/auth.py
Updated authors and changelof (#142)