Contour Expand / Contract Functionality (Issue #183)

Expansion:

    cam = Camera()
    i = cam.getImage()
    b = i.findBlobs()[-2]
    b.expand(6)
    b.show()

Contraction:

    cam = Camera()
    i = cam.getImage()
    b = i.findBlobs()[-2]
    b.expand(-5)
    b.show()