Progresses in docstringing the configurators

Doc/build_doc.sh

Doc/build_help.sh

Doc/conf_html.py

MDANSE/App/GUI/Framework/Plugins/AtomSelectionPlugin.py

...E/App/GUI/Framework/Plugins/DensitySuperpositionPlugin.py

MDANSE/App/GUI/Framework/Plugins/Plotter/PlotterPlugin.py

MDANSE/Core/Platform.py

MDANSE/Framework/Configurators/AtomSelectionConfigurator.py

.../Framework/Configurators/AtomTransmutationConfigurator.py

MDANSE/Framework/Configurators/AxisSelectionConfigurator.py

MDANSE/Framework/Configurators/BasisSelectionConfigurator.py

MDANSE/Framework/Configurators/FloatConfigurator.py

MDANSE/Framework/Configurators/FramesConfigurator.py

MDANSE/Framework/Configurators/GroupingLevelConfigurator.py

MDANSE/Framework/Configurators/IConfigurator.py