minor optimization of SURF_GPU (reduce memory transfers, use structure of arrays instead of array of structures)

[~] fixed warning in featuers2d under windows (can't generate assignment operator)

fixed compilation under Win64

added missing cudaSafeCall

fixed bugs in gpu::cvtColor

[~] Updated GPU module install target to copy NCV.hpp and NPP_staging.hpp to the package include directory

[+] Added 128-bit transpose

a big patch; use special proxy types (Input/OutputArray, Input/OutputArrayOfArrays) for passing in vectors, matrices etc.

added downsample function into gpu module, refactored it a little bit, added guard for CUDA related include in cascadeclassifier_nvidia_api.cpp

[~] Refactored, cleaned up, and consolidated the code of GPU examples (cascadeclassifier and cascadeclassifier_nvidia_api)

[*] Fixed #974 ("GPU CascadeClassifier fails with some training files"): Moved IsNodeLeaf bit from NodeDescriptor to FeatureDescriptor for both left and right nodes, therefore from now on max number of rects in a feature is 31