- broken bindings generator
- broken conversion functions (uses non-supported cv::Mat types)
- other problems like missing convertion functions for Moments and other structs

Otherwise we cannot find opencv2/opencv_modules.hpp, which is
located directly inside the CMAKE_BINARY_DIR.

This patch fixes Matlab binding generation for modules that are
part of opencv_contrib (xfeatures2d specifically), and are therefore
not located in ${CMAKE_SOURCE_DIR}/modules.

For this, gen_matlab.py script is extended to accept multiple values
for --modules-root argument, and to check for a module's header in
all possible paths. This way, both ${CMAKE_SOURCE_DIR}/modules and
${OPENCV_EXTRA_MODULES_PATH} can be passed as modules root paths,
and main header for xfeatures2d module is correctly located.