k1, k2, p1, p2 trackbar values need offset

Thanks for this example program. For distortion input I suggest this:
```python
	k1 = float(cv2.getTrackbarPos("K1",WINDOW_NAME))/100000. - 0.5
	k2 = float(cv2.getTrackbarPos("K2",WINDOW_NAME))/100000. - 0.5
	p1 = float(cv2.getTrackbarPos("P1",WINDOW_NAME))/100000. - 0.5
	p2 = float(cv2.getTrackbarPos("P2",WINDOW_NAME))/100000. - 0.5
```