calibration is started with the program (robot rotates around itself),
has to be stopped with a push on button left;
motor speed reduced, so the robot needs 40 seconds for 2 rotations now
added a thread that prints the current degrees for 20 seconds after the
calibration for 20 seconds; this allows us to check if the calibration
worked
Merge branch 'master' of https://github.com/MindstormsNXJ/mindstorms.git