linux build: take 3 :p

close issue #300
cmake: Fix RPATH/RUNPATH issue with openSuse wxWidgets libdir.

Gregory: Add an if clause to only change the rpath on openSuse

For me it doesn't follow the FHS => http://www.tldp.org/HOWTO/HighQuality-Apps-HOWTO/fhs.html
linux: add a desktop file that install PCSX2 on system menu

* Some people prefers emulator/system than emulator/game
Do commits 2bc2047 and f287754 the right way ...