These two typdefs are not compiled when BUILD_opencv_dnn is set to
false, however there are other modules that uses these typedef so
it may cause build errors. Moving typedef to the python module
ensures they are always defined.

Signed-off-by: Li Peng <peng.li@intel.com>

This statement was keeping HAAR cascades from leveraging opencl on nvidia devices. "localSize" on the featureEvaluator remains Size(0, 0) which sets the bool "use_ocl" to false. Adding this allows NVidia GPUs to leverage opencl HAAR Cascades

To avoid problem with reduced stack size of inner threads.

The original template based mat ptr for indexing is not implemented,
add the similar implementation as uchar type, but cast to
user-defined type from the uchar pointer.