LDEV-3115: Save LD preparations. Adapt ObjectExtractor so it reads from JSON. Add "Save" and "Save as" buttons. Allow choosing where to save the LD, along with some validation. Partial LD serialization.
LDEV-3115: Allow loading and remembering groups to branches mappings. Add Zoom Out button for presentation purposes. Add Canvas and Description tabs. Add a tip when user clicks Transition button. Multiple minor fixes.