Minor refactorings and improvements of tutorial interfaces and base classes.

...ng/kernel/ui/extension/base/TutorialStepUIAtomicBase.java

...extension/base/TutorialStepUIAtomicWithWhitelistBase.java

...kernel/ui/extension/base/TutorialStepUICompositeBase.java

...ension/base/TutorialStepUICompositeWithWhitelistBase.java

...fortiss/tooling/kernel/ui/internal/TutorialUIService.java

...oling/kernel/ui/internal/editor/TutorialStepUIEditor.java

.../kernel/ui/internal/editor/TutorialStepUIEditorInput.java

...fortiss/tooling/kernel/ui/internal/views/DoubleClick.java

...ernel/ui/internal/views/NavigatorTreeContentProvider.java

...fortiss/tooling/kernel/ui/service/ITutorialUIService.java