feature: Add notifications for users to make interaction lively

[Zafeeruddin]

Currently the reason why people not interact a lot on app is because of not having notifications on when someone interact with their problems

Notifications could be added on:

1. Notifying users on comments (including all users in the thread)
2. Notifying when users interact with questions.

The second one will be game changer, you would not need to purge questions page as mentioned in #1438.

Suggested architecture:

PS: I have already started working on it, will proceed to work if agreed upon.

[Zafeeruddin]

@hkirat @devsargam @siinghd

[deauthe]

looks like a great enhancement. Knowing that somebody's asking you a follow up question on a comment should be primitive behaviour. Upvotes