Inject discovered input filter into MvcEvent

- Once an input filter is discovered, it is now injected into the
  MvcEvent as the `ZF\ContentValidation\InputFilter` parameter, allowing
  retrieval later.
- Helps to address zfcampus/zf-apigility-admin#46
Merge branch 'hotfix/46'

Injects the MvcEvent with the input filter, if present.