CDK-474: CrunchDatasets by URI

This pull request builds on https://github.com/kite-sdk/kite/pull/98 adding changes to get Crunch sources and targets by URI.
Yeah, I will have the change posted in a minute.  If the instantiation gets delayed until job commit there is the downside that a problem with the URI may not be caught until after an MR job when it might otherwise have been caught before the MR job.  We could consider adding some additional upfront URI validation to try to further limit the likelihood of that type of problem but I imagine there are some types of URI issues that you might never really catch without actually trying to load the view.