Implemented Disable Mapsounds Plugin

I almost forgot posting this. A feature that has been requested by many players for months - a simple !stopsound command that disables all the map music.
I'm not sure about implementation, but someone programmed something already.
Adding a little rolling chat message that pops up every x minutes with "Map music can be disabled with !xxx" would be neat as well.

Edit: The plugin apparently uses !music, that is probably fine too - Now that I think about it, I've seen many players type !music in chat, thinking they were looking for the radio.