Adding color variable and destructive parseur to check variable presence.

Code is very ugly... Just check one variable not dynamicly;

:msg_type:$variable_name=value:msg to use an variable
Now xmixer use color variable.
If you mute an mixer, the volume is displaying in red. And if you
unmute display text is green
Code cleaning, and adding callback function to call for apply one variables
at the display time
Little modification for patch segmentation fault when you have not Xscreen...