Modernising the code, improving images

src/Cxx/Picking/AreaPicking.cxx

src/Cxx/Picking/CellPicking.cxx

src/Cxx/Picking/HighlightPickedActor.cxx

src/Cxx/Picking/HighlightPickedActor.md

src/Cxx/Picking/HighlightSelectedPoints.cxx

src/Cxx/Picking/HighlightSelection.cxx

src/Cxx/Picking/HighlightWithSilhouette.cxx

src/Cxx/Picking/HighlightWithSilhouette.md

src/Python/Picking/HighlightPickedActor.md

src/Python/Picking/HighlightPickedActor.py

src/Python/Picking/HighlightWithSilhouette.md

src/Python/Picking/HighlightWithSilhouette.py

src/Testing/Baseline/Cxx/Picking/TestAreaPicking.png

src/Testing/Baseline/Cxx/Picking/TestCellPicking_1.png

...Testing/Baseline/Cxx/Picking/TestHighlightPickedActor.png

src/Testing/Baseline/Cxx/Picking/TestHighlightPoints.png

...ting/Baseline/Cxx/Picking/TestHighlightSelectedPoints.png

src/Testing/Baseline/Cxx/Picking/TestHighlightSelection.png

...ting/Baseline/Cxx/Picking/TestHighlightWithSilhouette.png

...ting/Baseline/Python/Picking/TestHighlightPickedActor.png