bash: Store XBMC data in $XDG_DATA_HOME

This depends on the this patch [1] being accepted into the xbmc
mainline. Currently I am using a custom build including that patch, you
may find a Arch Linux PKGBUILD here [2].

 [1] https://github.com/xbmc/xbmc/pull/3867
 [2] https://github.com/EvanPurkhiser/PKGBUILDs/tree/master/xbmc