Deleting object prototype does not delete instances #25
Description
Several behaviors need to be implemented:
- On delete, issue a warning and confirmation dialog indicating that any instances in levels will be removed as well
- Enumerate all open levels and delete any matching instances
- Modify the level opening routine to check if the parent prototype of an object instance is missing, and if so, offer the user the choice of deleting the instances, or place them into a "hibernating" state. Such a state would be necessary to deal with a temporarily missing library, for example.