Extending stitching module

[ IMP : Please don't merge. It is in initial testing phase ] 

Trying to extend stitching functions to Python. Right now only most basic functionality of Stitcher class is extended. 
eg:
```
img1 = cv2.imread('974-1.jpg')
img2 = cv2.imread('975-1.jpg')

a = cv2.createStitcher()
ret, pano = a.stitch([img1,img2])
cv2.imwrite('pano.png', pano)
```