Added configuration menu for HUD functions: The V1 HUD has 4 functions (holes) which may be realized by one or two LEDs. The functions (like ppo2 monitoring or ascent speed) may be configurated by the diver using the HUD menu. The functions which may be selected depend on the HW configuration (e.g. the connected sensors) and the number of LEDs which are needed to realize the function. The previous HUD test implementation may still be activate usind the compile switch ENABLE_HUD_TESTING