Fix ndimage::concretize and ndimage::ch_value implementation

See merge request !37

# Conflicts:
#	doc/source/core.rst
#	doc/source/core/concepts/domains.rst
#	doc/source/core/concepts/pixels.rst
#	doc/source/core/concepts/ranges.rst
#	doc/source/core/domains.rst
#	doc/source/core/pixels.rst
#	doc/source/core/points.rst
#	doc/source/core/ranges.rst
#	pylene/CMakeLists.txt
#	pylene/include/mln/core/concept/new/cmcstl2.hpp
#	pylene/include/mln/core/concept/new/concepts.hpp
#	pylene/include/mln/core/concept/new/domains.hpp
#	pylene/include/mln/core/concept/new/indexes.hpp
#	pylene/include/mln/core/concept/new/pixels.hpp
#	pylene/include/mln/core/concept/new/points.hpp
#	pylene/include/mln/core/concept/new/ranges.hpp
#	pylene/include/mln/core/concept/new/values.hpp
#	pylene/include/mln/core/image/ndimage.hpp
#	pylene/include/mln/core/image/private/image_traits.hpp
#	pylene/include/mln/core/rangev3/private/multidimensional_range.hpp
#	pylene/include/mln/core/rangev3/range_traits.hpp
#	pylene/include/mln/core/rangev3/view/remove_if.hpp
#	pylene/include/mln/core/rangev3/view/reverse.hpp
#	pylene/include/mln/core/rangev3/view/transform.hpp
#	pylene/include/mln/core/rangev3/view/zip.hpp
#	pylene/include/mln/core/rangev3/view/zip_with.hpp
#	tests/core/CMakeLists.txt
#	tests/core/concept/domains.cpp
#	tests/core/concept/indexes.cpp
#	tests/core/concept/pixels.cpp
#	tests/core/concept/points.cpp
#	tests/core/concept/ranges.cpp
#	tests/core/concept/values.cpp
#	tests/core/range/multi_indices.cpp
#	tests/core/range/multi_span.cpp
#	tests/core/range/reverse.cpp
#	tests/core/range/transform.cpp
#	tests/core/range/zip.cpp

Image concept (PR2)

See merge request !33

ndimage models RawImage (propotype stride/data)

TODO revert des-ambiguous call in API usage

Fix unit tests image concept
Use archetype for all concept unit tests
Fix useless doc pages

Fix ambiguous calls

Fix archetypes name + writable concepts