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)
```

It gives me an error during compilation
```
In file included from /run/media/abidrahmank/OFFICE/repos/opencv/build/modules/stitching/precomp.hpp:59:0:
/run/media/abidrahmank/OFFICE/repos/opencv/modules/core/include/opencv2/core/ptr.inl.hpp: In instantiation of ‘cv::Ptr<T> cv::makePtr() [with T = cv::Stitcher]’:
/run/media/abidrahmank/OFFICE/repos/opencv/modules/stitching/src/stitcher.cpp:537:48:   required from here
/run/media/abidrahmank/OFFICE/repos/opencv/modules/stitching/include/opencv2/stitching.hpp:146:5: error: ‘cv::Stitcher::Stitcher()’ is private
```