store command-line arguments in bulletDemo.txt
save/load of configuration, save demo name instead of index
add setBackgroundColor as example (background_color_red) and
mouse move/wheel speed config (mouse_wheel_multiplier and mouse_move_multiplier)
(saved after changing the demo)
default btIDebugDraw colors can be changed
b3CommandLineArgs::GetCmdLineArgument returns bool, and b3CommandLineArgs::addArgs added
fix copy/paste
