Refactored UserManager and extended User model.
UserManager is now more DRY and handle more model fields.
User now has received some models previously found in import_users_from_csv.py.
They should be in the User model so they can be reused easily
Added tests for User.generate_password and is_existing.
I should probably consider  moving the generate_password to the
UserManager? I'm not entirely sure that static methods belong in a model
Fixed User.is_existing being a non-static method
Fixed a password=None parameter in UserManager.create_user
Added a CourseAssignment.is_existing static method and a test for that.
Added a refactored import users from csv script.
It's still rought at places, but it's a little bit more readeable than before.
For now, commented out a faulty forum test.
It should be researched why it fails on PostgreDB exclusively
Merge pull request #31 from HackBulgaria/import_csv

Refactor import_csv