Make fixture loader service locator aware

Small change to make fixture loader Service Locator-aware and inject it's SL instance into any SL-aware fixtures it loads.  

Rationale:  our fixtures use Faker to create mock data for testing purposes.  Rather than manually build the dependency chain for each entity I would like to pull in the ZF2 form where all that work has already been done and use that to create the test entities. 

See Issue #7