Added combined GPIS and GetVariance() to GPIS with normals.

VirtualRobot/CMakeLists.txt

VirtualRobot/math/GaussianImplicitSurface3DCombined.cpp

VirtualRobot/math/GaussianImplicitSurface3DCombined.h

VirtualRobot/math/GaussianImplicitSurface3DNormals.cpp

VirtualRobot/math/GaussianImplicitSurface3DNormals.h

VirtualRobot/math/GaussianObjectModelNormals.cpp

VirtualRobot/math/Kernels.cpp

VirtualRobot/math/Kernels.h

VirtualRobot/math/MathForwardDefinitions.h

...lRobot/tests/MathGaussianImplicitSurface3DNormalsTest.cpp

VirtualRobot/tests/MathGaussianImplicitSurface3DTest.cpp