Specify python version for qtile in xephyr script
Specify python version for qtile in xephyr script

For fast change between python version without
editing script itself introduced $PYTHON

Closes #936

kynikos/qtile,ramnes/qtile,tych0/qtile,kynikos/qtile,de-vri-es/qtile,frostidaho/qtile,soulchainer/qtile,de-vri-es/qtile,soulchainer/qtile,zordsdavini/qtile,ramnes/qtile,flacjacket/qtile,qtile/qtile,qtile/qtile,tych0/qtile,zordsdavini/qtile,flacjacket/qtile,cortesi/qtile,cortesi/qtile,frostidaho/qtile