[arch-dev-public] new pkg for extra: LXDM

LXDM had a nice stable release 0.3.0 a few weeks ago and is ready to use. It's the best light weight alternative we have next to gdm/kdm and slim/xdm. I know about Jürgens ask for help on lxde packages but I'd like to maintain lxdm in extra independent from lxde as an option for Xfce users. Any objections? -Andy