Upgrade to Entity Framework 6 Beta 1

* Upgrade the project to reference Entity Framework 6 Beta 1.
* InMemoryDbSet implements the new methods added to the IDbSet interface.
* Fix broken unit test. The test data is incorrect and the implementation of static/instance Data is inconsistently retrieving data their respective variables.

This is probably better suited to live in a separate branch until Entity Framework 6 is released but I can only do a pull request to an existing branch...