Use GlobalDbSingleton API on Android to update database in reponse to notifs in CommNotificationsHandler.

Summary: We use GlobalDBSingleton API in Java for two things: 1. Safely update database from CommNotificationsHandler.

Test Plan: Build the app, send notifications and rescinds. Ensure app is not crashing.

Reviewers: tomek, atul

Reviewed By: tomek

Subscribers: jon, ashoat, abosh

Differential Revision: https://phab.comm.dev/D5237