[PATCH] Add mumble

[ng0]

[PATCH] gnu: Add mumble.

I tested succesfully: configuration wizzard, connection to gnunet.org server.
I was not not able to test: actual interaction with other people, this will 
follow tomorrow afternoon/evening.

Shortcomings of this patch:
The images are CC licensed. I wasn't able to figure out the exact licenses and 
also not which images end up on the system. I do install knowingly only 1 image 
which is the icon.
The bundled celt sources need to be removed, at the moment they still get 
caught up in a check. From my theoretic understanding, opus is enough, as it 
includes most of what used to be in celt.