Exported a high level stitcher the DLL

allows Stitcher to be used for scans from within python.
I had to use very strange notation because I couldn't export the `enum`
`Mode` making the Cpython generated code unable to compile.

```c++
class Stitcher {
public:
enum Mode
    {
        PANORAMA = 0,
        SCANS = 1,
    };
...
```

Also removed duplicate code from the `createStitcher` function making
use of the `Stitcher::create` function

modules/stitching/include/opencv2/stitching.hpp

@@ -312,6 +312,7 @@ private:
 };
 
 CV_EXPORTS_W Ptr<Stitcher> createStitcher(bool try_use_gpu = false);
+CV_EXPORTS_W Ptr<Stitcher> createStitcherScans(bool try_use_gpu = false);
 
 //! @} stitching