CDK-474: CrunchDatasets takes Dataset or View URI
CDK-474: delay loading Dataset from URI
CDK-451: Add isReady, signalReady to views
CDK-451: Add signalReady() to DatasetKeyOutputFormat
CDK-451: Add signalReady() support to CrunchDatasets
CDK-451: Make signalReady() automatic instead of opt-in
CDK-451: Change ready signal filename to _SUCCESS