Added missing VirtualMachine import
Test are now working for db, logic modules
Move _get_costs (internal method) to credits.py
Internal method calculate_cost moved to utils.py
Move process_backend_msg to beckend.py
Moved id_from_instance_name static method to utils.py
Refactored charge (from VM model) and fixed unit tests
Moved SynnefoUser methods to logic.credits
Add logic app in django configuration
Initialise logic-refactoring branch