- Better logic to recursively link parent/children entities, so partial
updates won't get lost.
- Removed `EntitiesCache` - it was too much to maintain while keeping
consistent with the ORM, and it was a perennial fight against
SQLAlchemy's own cache.
- Removed `EntityNotifier` - with no need to merge cached entities, the
`notify` method has become much simpler and it's simply been merged
in the `EntitiesRepository`.
Fabio Manganiello