- Invalid generators (missing world, overlapped, generator template missing/broken) are now saved to the database and wait to be restored if they ever become valid again.

Explanation of the behavior
If you:
- Modify a generator YAML file and make a mistake
- Reload the plugin to apply changes
- Then that generator template will not load, and all placed generators in your world will be deleted.

But in the new version:
- The deleted generators are saved to the database as invalid_resources
- Now you have a chance to fix your mistake
- So when you reload the plugin all previously missing generators will be restored

- Refactoring and improvements to error/warning messages