Bug 25845 Support for manually attaching source to a class path container
From Dejan: There is a work item on the ability to manually attach source to classpath entries managed by classpath container. We discussed it and we have workable options but we would like if we can have it by M3 because we want to start self-hosting using classpath containers ourselves.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/LibrariesWorkbookPage.java
private static final String DIALOGSTORE_ADV_SECTION= "LibrariesWorkbookPage.advanced"; 
		private static final String DIALOGSTORE_SELECTED= "selected"; 
		private static final String DIALOGSTORE_CONTAINER_IDX= "containerindex"; 
		private DialogField fLabelField;
		private SelectionButtonDialogField fCreateFolderField;
		private SelectionButtonDialogField fAddFolderField;
		private SelectionButtonDialogField fAddContainerField;
		private ComboDialogField fCombo;
		private CPListElement[] fResult;
		
		private IDialogSettings fAdvSettings;
		
		private ClasspathContainerDescriptor[] fDescriptors;
		public AdvancedDialog(Shell parent) {
			super(parent);
			
			fAdvSettings= fDialogSettings.getSection(DIALOGSTORE_ADV_SECTION);
			if (fAdvSettings == null) {