Update sound support

Update sound support to use Qt4's phonon library, so that we can drop the dependence on pygame.

There is also the possibility of making (re)playing sounds more user friendly, by embedding a little loudspeaker icon in the card, which people then need to click. Since the cards support Javascript, this should not be too difficult. Look here for inspiration: http://www.phon.ucl.ac.uk/home/mark/audio/play.htm