The user definition can now be viewed from the user definition widget

MDANSE/Framework/Plugins/DataPlugin.py

MDANSE/Framework/Plugins/IPlugin.py

MDANSE/Framework/Plugins/UserDefinitionViewerPlugin.py

MDANSE/Framework/UserDefinitionsStore.py

MDANSE/Framework/Widgets/PartialChargesWidget.py

MDANSE/Framework/Widgets/QVectorsWidget.py

MDANSE/Framework/Widgets/UserDefinitionWidget.py

MDANSE/GUI/MainFrame.py

MDANSE/GUI/PluginsTreePanel.py