Support more opponents

[NaN]

Windows build(without data) vdrift-gui-2012-06-01.exe:
https://sourceforge.net/projects/vdrift/...%20builds/

Changes:
- Refactor GUI. Replace old widgets with few orthogonal components control, label, image, (slider). Expose gui componet properties to gui config files(gui pages), support some minimal script-ability. Construct complex gui widgets/functionality using available components. Load garage track as gui background.
- Fix: Set constant to floats explicitly to make vs compiler happy.
- Fix: Add new samplers before removal -> to follow add sources behavior.
- Fix: Make sure wheel position is updated if body position is set(SetPosition).
- GUI, GUIPAGE are extending passed actionmap. Pass a copy to avoid undefined behavior, isolate pages.



Another larger set of GUI changes. Garage(track) as background means GUI readability need to be addressed. Any ideas are welcome.

For anyone interested in playing with the GUI. It is quite configurable now. Assign gui reload key in Options/Controls/Game/Tools to reload the gui on the fly. For starters look into data/skins/simple/menus/Main. A somewhat more complex gui page is PracticeGame.

@Timo: I overwrote some of your gui skin fixes, sorry Will add them back asap.