Modernising the code, improving images

src/Cxx/PolyData/ExtractCellsUsingPoints.cxx

src/Cxx/PolyData/ExtractPolyLinesFromPolyData.cxx

src/Cxx/PolyData/ExtractSelectedIds.cxx

src/Cxx/PolyData/ExtractSelection.cxx

src/Cxx/PolyData/ExtractSelectionCells.cxx

src/Cxx/PolyData/ExtractSelectionOriginalId.cxx

src/Cxx/PolyData/ImplicitDataSetClipping.cxx

src/Cxx/PolyData/ImplicitModeller.cxx

src/Cxx/PolyData/ImplicitPolyDataDistance.cxx

src/Cxx/PolyData/ImplicitPolyDataDistance.md

src/Cxx/PolyData/ImplicitSelectionLoop.cxx

src/Cxx/PolyData/InterpolateMeshOnGrid.cxx

src/Cxx/PolyData/InterpolateMeshOnGrid.md

src/Cxx/PolyData/InterpolateTerrain.cxx

src/Cxx/PolyData/IntersectionPolyDataFilter.cxx

src/Cxx/PolyData/IterateOverLines.cxx

src/Cxx/PolyData/IterateOverLines.md

src/Python/PolyData/ExtractPolyLinesFromPolyData.md

src/Python/PolyData/ExtractPolyLinesFromPolyData.py

src/Python/PolyData/ExtractSelection.md