Add "mute" command

What should it do?

It should disable all kinds of notifications from a window for a configurable amount of time.

Motivation

Sometimes, a discussion in a room turns unhealthy. Ignoring individuals may not be useful there because multiple people are involved and you don’t want to ignore everyone forever.

Muting the conversation instead helps with focusing on different things; first because there isn’t the nagging number indicating unread content, second because alt+e and co will not jump to that room.

More info

• The mute time should be selectable at execution time, ideally with a pop-up UI so that one doesn’t have to remember an arcane syntax
• The default mute time should be configurable.