xBRZ texture scaling

Adds an option for 2x/3x/4x/5x texture scaling using xBRZ. Also includes a Windows UI for setting the option.

Tested and working on Wipeout Pulse, Corpse Party, Gurumin, Fate/Extra and Black Rock Shooter.

Fate/Extra - Before:
http://www.abload.de/img/ppssppdebug_2013_04_2z6o8b.png
Fate/Extra - After:
http://www.abload.de/img/ppssppdebug_2013_04_2rwsai.png

Wipeout - Before:
http://abload.de/img/ppssppwindows_2013_04n2fxf.png
Wipeout - After:
http://abload.de/img/ppssppwindows_2013_042od2v.png

Potential issues:
- I added the xbrz files to ext/, as that seemed like a good place to put them, but I didn't want to make a new project for a single source file so I added it to the GPU project. A bit messy.
- I did not update any CMake build files, as I couldn't get that build method to work on my system.