This allows subclasses of CvBoost to override initial weights that
update_weights uses without duplicating its entire implementation.

This reverts commit 4d36be87.

Conflicts:
	modules/ml/include/opencv2/ml/ml.hpp
	modules/ml/src/data.cpp

This reverts commit 618fbf55.

added opencv_world module that combines all the other [selected by user] OpenCV modules, except for opencv_python and opencv_gpu.

python cv2 MLP sample done

minor fixes in CvGBTrees, its test and sample