* Integrate the new ui.MenuBar into the Editor Scene.
* File: New Level/Doodad, Save [as], Open, Close, Exit
* Edit: Undo, Redo, Level options
* Level: Playtest
* Tools: Debug overlay, Command shell
* Help: User Manual, About
* Add an About dialog accessible from the Help menu.
* Update code for recent changes in UI toolkit around event handlers for
buttons.
* Add tooltips to various buttons in the Editor Mode. The left toolbar
shows the names of each tool, the Doodad Palette shows the title of
each doodad and the Color Palette shows the swatch attributes (solid,
fire, water, etc.)
