Rhythmbox 3.0.x compatibility: use python3

Hi again :-)

the new rhythmbox 3.0 release ( http://ftp.acc.umu.se/pub/GNOME/sources/rhythmbox/3.0/ ) 
uses python3 for plugins ( see http://ftp.acc.umu.se/pub/GNOME/sources/rhythmbox/3.0/rhythmbox-3.0.news ).

I used 2to3 to make sure all python scripts are compatible with python3 and reindent.py to fix indentations afterwards.