Move legacy part of opencv_contrib to separate header
Drop old python interface
Drop old python samples and tests
Remove documentation for old python wrapper
Turn pyopencv_to and pyopencv_from into templates

This protects from unwanted implicit conversions between types at compile time.
Merge pull request #809 from taka-no-me:drop_python1
Minimize usages of legacy C API inside the library
Merge pull request #824 from taka-no-me:reduce_c_api_deps
Merge branch '2.4'