Deep-link user to applications settings when they try to enable notifications for a thread without notifications enabled globally for Comm application.

Summary: Set state of {ush Notifs Switcher based on notifications permissions and prevent changing it if notifications permissions are not granted. Finally deep-link user to application settings if the try to change it when notifications permissions are not granted. It must be noted however that whether notifications are enabled in general is not reflected in threadInfo.currentUser.subscriptions in database.

Test Plan: Build app, disable/enalbe notifications in settings and check whether switcher state is correct and whether deep-link alert is shown when notifications are disabled.

Reviewers: palys-swm, def-au1t, ashoat

Reviewed By: palys-swm, def-au1t, ashoat

Subscribers: ashoat, Adrian, atul, benschac, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3565