Devicemanager Changes

It is not necessary any more to start / stop the devicemanager. This is
done by its own now. It automatically stops when adding / removing a
device and starts afterwards again.
Fix really nasty bug

Sometimes a device would not be able to get any rawvalue, because any
read would simply return bytes from the serial buffer, which could
include bytes from another device. This is now fixed as in changeInput a
ser.flushInput() is called.