Add NuGet package definitions (reverse engineered)

[nietras]

• Prefix packages with nietras.
• Package contents are defined as below, but dlls are not commited to git, everything else is.

+---nietras.cntk.deps.cuda
|   |   nietras.CNTK.Deps.Cuda.nuspec
|   |
|   +---build
|   |   +---native
|   |   |       nietras.CNTK.Deps.Cuda.targets
|   |   |
|   |   \---netstandard2.0
|   |           nietras.CNTK.Deps.Cuda.targets
|   |
|   \---support
|       \---x64
|           \---Dependency
|                   cublas64_10.dll
|                   cublasLt64_10.dll
|                   cudart64_102.dll
|                   curand64_10.dll
|                   cusparse64_10.dll
|                   nvml.dll
|
+---nietras.cntk.deps.cudnn
|   |   nietras.CNTK.Deps.cuDNN.nuspec
|   |
|   +---build
|   |   +---native
|   |   |       nietras.CNTK.Deps.cuDNN.targets
|   |   |
|   |   \---netstandard2.0
|   |           nietras.CNTK.Deps.cuDNN.targets
|   |
|   \---support
|       \---x64
|           \---Dependency
|                   cudnn64_7.dll
|
+---nietras.cntk.deps.mkl
|   |   nietras.CNTK.Deps.MKL.nuspec
|   |
|   +---build
|   |   +---native
|   |   |       nietras.CNTK.Deps.MKL.targets
|   |   |
|   |   \---netstandard2.0
|   |           nietras.CNTK.Deps.MKL.targets
|   |
|   \---support
|       \---x64
|           \---Dependency
|                   libiomp5md.dll
|                   mkldnn.dll
|                   mklml.dll
|
+---nietras.cntk.deps.opencv.zip
|   |   nietras.CNTK.Deps.OpenCV.Zip.nuspec
|   |
|   +---build
|   |   +---native
|   |   |       nietras.CNTK.Deps.OpenCV.Zip.targets
|   |   |
|   |   \---netstandard2.0
|   |           nietras.CNTK.Deps.OpenCV.Zip.targets
|   |
|   \---support
|       \---x64
|           \---Dependency
|               |   zip.dll
|               |   zlib.dll
|               |
|               +---Debug
|               |       opencv_world310d.dll
|               |
|               \---Release
|                       opencv_world310.dll
|
\---nietras.cntk.gpu
    |   nietras.CNTK.GPU.nuspec
    |
    +---build
    |   +---native
    |   |   |   nietras.CNTK.GPU.targets
    |   |   |
    |   |   +---include
    |   |   |   |   CNTKLibrary.h
    |   |   |   |   CNTKLibraryC.h
    |   |   |   |   CNTKLibraryExperimental.h
    |   |   |   |   CNTKLibraryInternals.h
    |   |   |   |   HalfConverter.hpp
    |   |   |   |
    |   |   |   \---Internals
    |   |   |           ComputationGraphAlgorithms.h
    |   |   |           EvaluatorWrapper.h
    |   |   |           PrimitiveFunction.h
    |   |   |           PrimitiveFunctionAttribute.h
    |   |   |           PrimitiveOpType.h
    |   |   |
    |   |   \---lib
    |   |       \---x64
    |   |           +---Debug
    |   |           |       Cntk.Core-2.7.1d.lib
    |   |           |
    |   |           \---Release
    |   |                   Cntk.Core-2.7.1.lib
    |   |
    |   +---netstandard2.0
    |   |       nietras.CNTK.GPU.targets
    |   |
    |   \---non-supported
    |       \---include
    |               CNTKLibrary.h
    |
    +---lib
    |   \---netstandard2.0
    |           _._
    |
    \---support
        \---x64
            +---Debug
            |       Cntk.Composite-2.7.1d.dll
            |       Cntk.Core-2.7.1d.dll
            |       Cntk.Core.CSBinding-2.7.1d.dll
            |       Cntk.DelayLoadedExtensions-2.7.1d.dll
            |       Cntk.Deserializers.Binary-2.7.1d.dll
            |       Cntk.Deserializers.HTK-2.7.1d.dll
            |       Cntk.Deserializers.Image-2.7.1d.dll
            |       Cntk.Deserializers.TextFormat-2.7.1d.dll
            |       Cntk.Math-2.7.1d.dll
            |       Cntk.PerformanceProfiler-2.7.1d.dll
            |
            \---Release
                    Cntk.Composite-2.7.1.dll
                    Cntk.Core-2.7.1.dll
                    Cntk.Core.CSBinding-2.7.1.dll
                    Cntk.DelayLoadedExtensions-2.7.1.dll
                    Cntk.Deserializers.Binary-2.7.1.dll
                    Cntk.Deserializers.HTK-2.7.1.dll
                    Cntk.Deserializers.Image-2.7.1.dll
                    Cntk.Deserializers.TextFormat-2.7.1.dll
                    Cntk.Math-2.7.1.dll
                    Cntk.PerformanceProfiler-2.7.1.dll