CMakesLists.txt : should be include liblxqt libs.

CMakesLists.txt should include liblxqt.
Especially for /usr/include/lxqt/LXQt/* , this code is necessary.

See https://github.com/lxde/lxde-qt/issues/177 .
Change greeter default background to black. Looks IMO better.
Clean up includes
Move loginform default position left