Add libSGM into cudastereo

[sotsuka-fixstars]

Merge with extra: opencv/opencv_extra#826

We are developers of libSGM, a CUDA implementation of Semi-Global Matching.
This PR adds libSGM into cudastereo module.

The orginal algorithm is described in [1].
For matching cost, the center-symmetric census transform [2] is used.

[1] Heiko Hirschmuller. Stereo processing by semiglobal matching and mutual information. Pattern Analysis and Machine Intelligence, IEEE Transactions on, 30(2):328–341, 2008.
[2] Robert Spangenberg, Tobias Langner, and Raúl Rojas. Weighted semi-global matching and center-symmetric census transform for robust driver assistance. In Computer Analysis of Images and Patterns, pages 34–41. Springer Berlin Heidelberg, 2013.

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[alalek]

Looks good to me! Thank you for contribution 👍

[Hunkzer]

Hi. Great implementation. Will this be available in opencv 3 also?

[alalek]

opencv 3

OpenCV 3.x is in the maintenance mode.
New functionality should not be added there.