XBMC RetroArch integration and some cores

This adds some additional retroarch cores as well as a script generation package to be used in conjunction with XBMC and the AdvancedLauncher addon, making it possible to use XBMC as an emulator frontend.
I think the name change is warranted since it is more user friendly to name the wrapper "xbmc" and not something like "xbmc-wrapper". @lethalman and I had the same discussion regarding the retroarch and its cores declarations.