Proper group and user schema

Fresh installs should work out of the box.
Migration instructions for existing installs:
db.users.update_many({}, {'$set': {'created': datetime.datetime.utcfromtimestamp(0), 'modified': datetime.datetime.utcnow()}})
db.groups.update_many({}, {'$set': {'created': datetime.datetime.utcfromtimestamp(0), 'modified': datetime.datetime.utcnow()}})

Tune up jobs API

delivered at:
 - GET /schema/group => POST schema
 - GET /schema/group?method=put => PUT schema