Added SyncFieldMixin

Added `SyncFieldMixin` + some additional logic in order to keep selected fields in sync between `Device` and `Asset` models.

Added 'service catalog' lookup and 'enviroment' choice field to the 'device info' form.
In my opinion here should be one method that specifies something like that:
``return [(obj1, [field1, field2]), (obj2, [field1, field3])]``

Whole mechanism will be more flexible...