First working version.

Commands tested:
 - play/pause
 - volume up/down

Program organised to use different terminal multiplexer
and potentially complex actions.
Add support for multilanguage and config file

New Language class manage *.lng files, that contain
<keyword, translation> pairs (using the syntax of 
java.util.Properties). A new configuration key 'language'
is added to configurations to specify the language to use.

Configuration file now can read custom values from a file
named "config.conf" located in the current folder (the one
where the client was launched from)