CDK-472: Add Datasets.URIBuilder
CDK-474: CrunchDatasets takes Dataset or View URI
CDK-451: Add isReady, signalReady to views
CDK-451: Add signalReady() to DatasetKeyOutputFormat
CDK-451: Add signalReady() support to CrunchDatasets
CDK-472: Fix test failure

Datasets.URIBuilder test was failing due to a minor difference in the
Dataset URI format from my original branch to Ryan's CDK-453 branch.
CDK-472: Return URI as URI instead of String