Add Sample Model with UnitTest

Hi,

I have created a sample test that could be a good starting point. 

Changes:

1. Created sample Model, with two entities: Pokemon and Type.
2. Created sample test
3. Changed extensions visibility to public, to allow framework use.
4. Added completionHandler (default values is nil) in findAllWithPredicate and findFirstOrCreateWithPredicate. The completion handler is necessary to allow async test and it should be added to all the function that call findAllWithPredicate or findFirstOrCreateWithPredicate
5. Added SuperRecordTestsTestCase : XCTestCase, ovveriding setUp function initializing the test managedObjectContext.