- added HAL documentation support
- added documentation to HAL replacement interface
- updated several HAL functions in imgproc module

The HAVE_DOC_GENERATOR variable was always true.

(cherry picked from commit 3d46c1f9)

Conflicts:
	doc/CMakeLists.txt

The HAVE_DOC_GENERATOR variable was always true.

- updated existing Doxyfile.in
- added corresponding cmake instructions
- added some specific files (layout, icon)
- clean existing doxygen warnings

Conflicts:
	CMakeLists.txt
	doc/CMakeLists.txt
	modules/core/include/opencv2/core.hpp
	modules/core/include/opencv2/core/base.hpp
	modules/core/include/opencv2/core/cuda.inl.hpp
	modules/core/include/opencv2/core/mat.hpp
	modules/core/include/opencv2/core/matx.hpp
	modules/core/include/opencv2/core/types.hpp
	modules/flann/include/opencv2/flann/lsh_table.h
	modules/imgproc/include/opencv2/imgproc.hpp

- updated existing Doxyfile.in
- added corresponding cmake instructions
- added some specific files (layout, icon)
- clean existing doxygen warnings

If both Python 2 and Python 3 are found, then build bindings for both of
them during the build process.  Currently, one version of Python is
detected automatically, and building for the other requires changes the
CMake config.

The largest chunk of this change generalizes OpenCVDetectPython.cmake to
find both a Python 2 and Python 3 version of Python.  Secondly, the
opencv_python module is split into two modules, opencv_python2 and
opencv_python3.  Both are built from the same source. but for different
versions of Python.

(cherry picked from commit b75cbfde)

Conflicts:

	cmake/OpenCVModule.cmake

The main problem with extra modules is that they're located outside
of the OpenCV root, while Sphinx requires that all documents are
within the documentation root. To circumvent this, we create a
"fake root" and copy all documentation (as well as all files that
it depends on) there. It's a bit messy, but what can you do.

As a bonus, this eliminates the need to generate modules/refman.rst
inside the source tree.

Aligned strings in CMakeList

Modified the check on plantuml extension

Some fixes

Moved find_host_program for plantuml script