CDK-451: View isReady / signalReady

This PR builds on https://github.com/kite-sdk/kite/pull/98 and https://github.com/kite-sdk/kite/pull/99 adding support for isReady / signalReady on Views.
Sorry, I'm not sure I quite follow this comment - can you elaborate?  I had previously added a commitJob method to NullOutputCommiter that would call signalReady() but the method was never actually called.

Also, I think the explanation "because..." is throwing me off.

I can't quite figure out quite what change exactly I should make nor exactly why.