Use the new libqtxdg environment neutral API

The non desktop neutral methods are deprecated now. Use the new ones.

Check:
https://github.com/lxde/libqtxdg/commit/aad8295dee5425b6a877bc0d232e58011b09cb89
http://git.lxde.org/gitweb/?p=lxde/libqtxdg.git;a=commit;h=aad8295dee5425b6a877bc0d232e58011b09cb89

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Merge branch 'adapt-to-libqtxdg-neutral-env-api'

* adapt-to-libqtxdg-neutral-env-api:
  Use the new libqtxdg environment neutral API