Adding ApiController.Validate : Fixes #1286

cc @rynowak 
should we make GetMetadataForType also take the value/entity directly? We keep creating these unnecessary closures all over the fx.

Chatted with @GrabYourPitchforks and he vaguely remembers that we had a reason in the past to do this before binding actually happened.

Perhaps we should add another overload. But before doing any changes, lets follow up with @GrabYourPitchforks 

CC @rynowak @pranavkm