Added cv2.boxPoints() functionality to Python bindings (Feature #2023)

http://www.code.opencv.org/issues/2023

eg:

In [3]: box = ((10,10),(5,5),0)

In [4]: cv2.boxPoints(box)
Out[4]:
array([[  7.5,  12.5],
       [  7.5,   7.5],
       [ 12.5,   7.5],
       [ 12.5,  12.5]], dtype=float32)
Added missing python functions in highgui documentation

setMouseCallback
createTrackbar