admin: Remove admin modifications

Remove modifications from webproject and astakos.
admin: Use a different function to get user quotas

Instead of defining our own, we can use the `list_user_quotas` function
of im.quotas. The only difference that this function has is that it
expects a list of users. In our case, we just create a list of one
item.
Merge branch 'feature-admin-quotas' into feature-admin
admin: Recognize Django "auth" app in router

The "Group" model comes from the auth app of Django. Add this to the
list of apps that will be handled by the 'astakos' db.
admin: Remove admin modifications

Remove modifications from webproject and astakos.
admin: Use a different function to get user quotas

Instead of defining our own, we can use the `list_user_quotas` function
of im.quotas. The only difference that this function has is that it
expects a list of users. In our case, we just create a list of one
item.
Merge branch 'feature-admin-router' into feature-admin