Push notification

[julianraj]

@tyohan we have issue regarding push notifications in web app..

In case of mobile app, users are subscribed to topics and we send notifications using the topics.
But web app doesn't support subscribing to topics. We need to register ids for each browser in the server and send notifications to these ids. For this, we will need API to register the registrations ids to the server and also change the notification-setup in the CMS to add support for web-app as well.

[tyohan]

For now we're not focus on notification. So I think we can put low prio on this issue. I will discuss with Prashant later about this.