ENH: make UserProfile compatible with django 1.5

Django 1.5 deprecates AUTH_PROFILE_MODULE settings which enable to extend User model.

scipy central UserProfile fields are not used in User authentication or Registration! So, a OneToField with User module fits our requirement. It is described at https://docs.djangoproject.com/en/1.5/topics/auth/customizing/#extending-the-existing-user-model

The following are the changes done:

1. remove AUTH_PROFILE_MODULE variable in settings
2. Improve UserProfile admin interface
3. change `User` model import