Unit test user app

* adds unit test for User model and forms
* refactors functions from user_checks.py into User class and drops user_checks.py

compensation/models/payment.py

@@ -10,8 +10,6 @@ from django.db import models
 
 from intervention.models import Intervention
 from konova.models import BaseResource
-from konova.utils.message_templates import PAYMENT_REMOVED
-from user.models import UserActionLogEntry
 
 
 class Payment(BaseResource):