Modify commCoreModule to use GlobalDBSingleton instead of creating its own thread

Summary: This differential modifies CommCoreModule to use GlobalDBSingleton instead of creating its own thread.

Test Plan: Build the app. The fact thst it works is a test since it changes the way JS accesses database

Reviewers: atul, tomek, jon

Reviewed By: tomek, jon

Subscribers: ashoat, abosh

Differential Revision: https://phab.comm.dev/D5232