#1344 #1366 New structure for email notification

Targets #1344 (closed) #1366 (closed)

Summary

1. New structure for user notification option and notification digest
2. Updates to cron to read from notification digest table and send notifications
3. Updates to global chat notification preference to save and read from notification user option
4. User Activity Tracker component added that is made generic and reusable
5. Used user activity tracker inside chat component to mark the channel activity for the user
6. Setting actioned=true for channels where user is active