* Add watchOS support for GoogleDataTransport with specifying notification center and WKExtensionDelegate for watchOS application, handling background tasks and network reachability flags on watchOS.
* Add independent watchOS test app for GoogleDataTransport and GoogleDataTransportCCTSupport.
* Add companion watchOS test app and notification service extension for GoogleDataTransportCCTSupport.
* Change removeItemAtURL to removeItemAtPath
It seems to work better, for reasons that aren't clear. It may have something to do with forming URLs being more strict.
* Add logging levels, fix failed write events
* Update comment