* refactors base attributes created and deleted into UserActionLogEntry foreign keys
* refactors all related queries and process logic
* fixes binding_on into binding_date in intervention/detail/view.html
* adds basic __str__ for some models
*
* adds UserActionLogEntry model to user/models.py
* wraps user and timestamp info
* can be extended for more information in the future
* refactors all filtering and accessing on values