Support Notification Scraping

[rspier]

It would be cool if G-Watch-Wear natively supported extracting BGs from tray notifications. XDrip+ does this already, but having to run both XDrip+ and G-Watch-Wear just causes extra battery drain. (And XDrip+'s implementation seems to have high update latency or some other sort of fuzziness.)

Here's an example of how to use NotificationListenerService: https://github.com/Chagall/notification-listener-service-example.

The XDrip+ code is in app/src/main/java/com/eveningoutpost/dexdrip/services/UiBasedCollector.java in their repo. (But it's GPL, so can't be directly used in G-Watch-Wear.)

Thanks-