Add Fluid Mapper

The implementation of our fluid mapper is mostly done:

• Implement fluid rendering pipeline: depth render + filter, thickness render + filter, surface normal generation, and composition
• Implement API with various get/set parameters
• Usage of parameters should be clearly stated in the doxygen of the vtkOpenGLSphereMapper.h file
• Implement nice examples with turning parameters inside the TestFluidMapper.cxx file
• Write a blog for fluid mapper
• Lighting now is computed from VTK lights
• Added access to environment map (cube map)

Here are several things that need to be continued by you, and the only incomplete shader is vtkFluidMapperFinalFS.glsl:

• We may need to be rewritten the examples in TestFluidMapper.cxx into a separate DemoFluidMapper.cxx and publish it on the vtk example website

Any further optimization is welcome.