Undo/Redo buttons, refactor menu toggles (#793)

* Make Undo & Redo and the menu buttons into actions; add undo/redo buttons

* Create variables for the ToolIcon colors

* Darken the menu buttons when they’re active

* Put the more intensive test in `perform`

* Fix & restyle hint viewer

* Add pinch zoom for macOS Safari

* Chrome/Firefox trackpad pinch zoom

* openedMenu → openMenu

* needsShapeEditor.ts → showSelectedShapeActions.ts

* Call showSelectedShapeActions

src/appState.ts

@@ -30,7 +30,7 @@ export function getDefaultAppState(): AppState {
     isResizing: false,
     selectionElement: null,
     zoom: 1,
-    openedMenu: null,
+    openMenu: null,
     lastPointerDownWith: "mouse",
   };
 }