See: paraview/paraview#22392

ColorMapToLUT_JSON now reads JSON files with multiple color maps.

The JSON colormap parser can now read from JSON files containing more than one colormap. More fixes to the parsing of colormaps done.

this addresses #308

1. Modified the imports
2.Background to SlateGray
3.default size to default
4.modified the arg parse help

`vtkImagingFactory` was removed in VTK version 6, but this example runs
just fine with any reference to that class removed.

1) Simplified the regular expressions
2) Comments in the examples are now handled correctly
3) C++ interface and implementation files are separately processed