Arcade physics mode

The new mode with arcade physics has been added to the game. It is much simpler to control bike in this mode, you even does not require a joystick, just keyboard and mouse (mouse with pressed right button can control left/right turn channel and forward/backward tilt channel, release button to center channels). With arcade mode you can stand still and ride slow without falls. Also you can explore all territory outside main courses (if the pedaling force will be large enough). Except arcade mode a possibility to set controls sensitivity by editing controls_settings.txt file was added. Bike suspension setup is also updated to make bike behaviour more stable both in simulator and arcade modes. If you had problems with rendering of the ground and sky on the Radeon GPUs in the very first version, then this release should also fix these problems.