Fixes and cleanup

- Fix Persistence\Memory internal storage to properly namespace instances with the same ID but of different classes.
- Remove fetching properties from db feature, because it was not possible to easily add missing static configuration during runtime and traits cannot override nor hint static properties when the consuming class also defines them.
- Fix docblocks.
- Cleanup tests.
- Allow for testing multiple classes in persistence tests.
- Add test for auto deriving table name from model class name.