Enable database initialization without starting JS on iOS

Summary: Initialize database before JS on iOS and create utility function that can be used in different callbacks whenever database access is needed - (didReceiveRemoteNotification in particular)

Test Plan: Build iOS app an real device, call this utility function from notification handling callback in every posssible app state: foreground, background and inactive. In each case examine logs to see that database is corectly initialized and accessible.

Reviewers: palys-swm, atul, ashoat

Reviewed By: palys-swm, ashoat

Subscribers: benschac, ashoat, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3297