IMPROVEMENT: use single PTU command to get the 4 position/speed values in spinCallback

[marklewis3000]

In node.cpp, in Node::spinCallbach(), 4 separate calls are made to get the pan and tilt positions and speeds, but (at lease for the D48E) a single command 'BT' will return the same results on one line. This will help prevent the returned data from getting out of step with the requests, which I have observed or even crashing.