manual control changed

the GPIO.add_event_detect is not reliable!!
thus put the start/stop-motor routine in a thread

controller.py: error correction in apply_object

halt.py: really call the system halt

gpio.py: prototype for wait_for_edge routine
setup:
  install icons in different sizes

client:
  simplify gui (just leave the necessary widgets)

server:
  typo in defaults-file
  do not produce any gpio signal when not running on pi