Allow to pass resource as context to input filter

Hi,

This is the associated PR to https://github.com/zendframework/zf2/pull/6154 and https://github.com/doctrine/DoctrineModule/pull/406

It allows to implement things like an update form that has a field that must be unique (email). Because ZfrRest directly fetches an entity, having this entity as context allows to such validators to work.

ping @danizord