Refactoring Northwind and OptimisticConcurrency functional tests

Split Northwind model into separate files and added a context class
Avoiding sharing any state between the contexts that mutate the model or the data
Renamed provider-specific test classes to include the provider name
Cleaning leftover databases
This is interesting. How often do you think this will fail as used by these tests, if you have any idea of that? Also, can you file a bug to look into integer generation for ATS that is suitable for production code?