startlxqt: Set proper prefix for XDG_DATA_DIRS
startlxqt: Set proper prefix for XDG_DATA_DIRS

initiated by @krytarowski and  discussed in lxde/lxqt-common#24

lxde/lxqt-session,stefonarch/lxqt-session,stefonarch/lxqt-session,lxde/lxqt-session,stefonarch/lxqt-session,lxde/lxqt-session