[DEV-1152] Add manager to AskbotUser. Further manager development is on hold - experimenting with PassThroughManager from django-model-utils.
[DEV-1152] Add django-model-utils to both requirements.txt.
[DEV-1152] Replace AskbotUserManager with PassThroughManager & custom AskbotUserQuerySet.
[DEV-1152] Move migrations to migrations_bak.
[DEV-1152] Add new initial Askbot migration.
[DEV-1152] Add custom AskbotUserPassThroughManager with create_user and create_superuser methods.
[DEV-1152] Add inheritance from UserManager to AskbotUserPassThroughManager.
[DEV-1152] Modify test utils.py create_user method to create an AskbotUser.
[DEV-1152] Change arguments to keyword arguments in AskbotUserPassThroughManager's create_user and create_superuser calls.
[DEV-1152] Remove __init__ method from AskbotUser and update post_save signal accordingly.
[DEV-1152] Update __getattr__ of AskbotUser to raise informative exceptions and only check for public User attributes.
[DEV-1152] Add custom create_user and create_superuser implementations to AskbotUserPassThroughManager.
[DEV-1152] Remove leftover break point from utils.py in tests.
[DEV-1152] Change mention of self.model to User explicitly.
[DEV-1152] Add normalize_email call to create_user method.