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.

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
• The PR is proposed to proper branch
• There is reference to original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented
• and sample code can be built with the project CMake

force_builders=Custom
buildworker:Custom=linux-4
build_image:Custom=ubuntu-cuda:16.04