More mobile tweaks (#790)

* Disable text selection

* Set content-editable=plaintext-only to disable Touch Bar formatting buttons

* Enlarge resize handle tap targets for pen/touch

* Make the lock button a button in mobile mode

* Use icons instead of Unicode characters; add an alternate toolbar for creating multipoint lines

* Allow buttons to hide themselves

* Fix heuristic for showing shape actions

* Refactor icons

* Fix label for edit button

* Switch edit button icon

* Remove lock button on mobile

* Add language selector on mobile

* Fix showing edit button on mobile

* Fix showing edit button on mobile, part 2

* Fix handle touch regions

* Fix scroll-back button position

* Allow using the text tool on a text object to start editing it

* Fix deletion of last point in line

src/components/ProjectName.tsx

@@ -36,7 +36,7 @@ export class ProjectName extends Component<Props> {
     return (
       <span
         suppressContentEditableWarning
-        contentEditable="true"
+        contentEditable={"plaintext-only" as any}
         data-type="wysiwyg"
         className="ProjectName"
         role="textbox"