[feature request] Mark all as read

With the current version of the app, many times, when a new message comes in, we'll just have a look the notification or the summary inside the app, but it's of no use entering the chat if the message is short. But the problem is that the number of "non-read" messages piles up.

There is currently now way to mark all messages as read, and when they are old and in the middle of many other messages, it is very tedious to open them all one by one.

We should have a "Mark all as read" function, and a possibility to sort messages by read status.