Remove sensor_gyro.c's dependency on mw.h/board.h.
BUGFIX - gyro calibration too short when movement detected during
calibration.

When the model is moved during the gyro calibration period too much the
code that detects the movement (gyroMovementCalibrationThreshold aka
'moron threshold') did not restart the calibration correctly and one too
few calibration cycles were used when restarting.

In addition to this there was unnecessary calibration reset code - the
reset of calibration variables is supposed to happen at the start of
calibration; due to the bug the first calibration cycle could not be
detected when restarting so the old reset code was required. 

This commit also cleans up the Gyro code so the it is in a similar style
to the recently cleaned acceleration code.