Viz initial backport, compilation fixes, moved viz/viz.hpp header according to 2.4 style
fixed documentation warnings
added guard to prevent linking VTK with Qt5
VTK off by default
rewrote perf tests for SURF
turn on CUDA part of nonfree module on Android for non-dynamic build
turn on CUDA part of stitching module on Android for non-dynamic build
update stitching sample
Merge pull request #2259 from ilya-lavrenov:ocl_surf
Merge pull request #2261 from jet47:stitching-cuda-android
Merge pull request #2178 from Nerei:viz_backport