robot.py: add debug statements, sanitize PWM channels

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
Adafruit_PWM_Servo_Driver.py: sanitize channel numbers

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
Add 'MoveForward' move

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>