This adds a counter of how many unread notifications are in this room on the room list.

Type: add

BUG: https://iron.lily-is.land/T52

Depends-on: https://iron.lily-is.land/D106 , https://iron.lily-is.land/D107

Send a message from another user that will generate a notification (e.g. by mentioning the current user). Verify that on the room list view there is a circle which contains the number 1. Open the room and verify that the number 1 disappears.