Update specs to enable mocking
Merge pull request #54 from MageTest/feature/fix-date-issue-for-product-fixture

Add created at to all products created
Fixtures now injected into Factory and maintain state

All fixture classes are now injected to the FictureFactory using the service
configuration. Each fixture now maintains state of the core model it
operates upon meaning reduced need to load resources and evaluate IDs.
Additional excpetion handling and validation is introduced.