wheezy-stage4-lxde-edu: don't use hardcoded user path for python_games launcher
wheezy-stage4-lxde-edu: don't use hardcoded user path for python_games launcher

Closes #128. It's arguable whether this is a major improvement, because of
course someone could copy across Desktop/* and before the link would have
still worked, but after this change it wouldn't if they didn't have
python_games in their home directory.

MrNice/spindle,asb/spindle,RPi-Distro/spindle,thusoy/spindle