Add bidirectional association support for embedded entities.

* Modify test cases to check inverse links work for one-to-many and one-to-one.
* Modify mapping strategy class to use same bidirectional code for embedded and non-embedded.
* Prevent infinite recursion saving embedded entities with bidirectional associations.
* Implement code to fix-up back-links when loading embedded entities.


Test suite passes for MongoDB and nothing else seems to have been broken.
I will run the contributor agreement past my employers and hopefully get it back to you soon.