[Chrome Support] [Research] Adding manifest.json

[safwanrahman]

Chrome needs manifest.json to be available in the page while asking for Push notification registration. Otherwise it will throw a error

Uncaught (in promise) DOMException: Registration failed - manifest empty or missing

So for adding support for chrome, we need to add a menifest.json to the directory. An example of menifest.json can be found here. The instruction can be found in MDN

In the menifest.json there is a field for gcm_sender_id. This can be obtained from the google console.
It should be possible for the developer to configure the gcm_sender_id in the settings so that its possible to get it from there.

We should find out a way to get it from settings and generate a json so that it will be possible to load the json in the page with the templatetags

[safwanrahman]

Fixed with f99c621