Adding the DisplacementPlot example.

src/Cxx.md

src/Cxx/VisualizationAlgorithms/CMakeLists.txt

src/Cxx/VisualizationAlgorithms/DisplacementPlot.cxx

src/Cxx/VisualizationAlgorithms/DisplacementPlot.md

src/Python.md

src/Python/VisualizationAlgorithms/DisplacementPlot.md

src/Python/VisualizationAlgorithms/DisplacementPlot.py