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/locales/en.json

@@ -40,7 +40,8 @@
     "colorPicker": "Color picker",
     "canvasBackground": "Canvas background",
     "drawingCanvas": "Drawing Canvas",
-    "layers": "Layers"
+    "layers": "Layers",
+    "language": "Language"
   },
   "buttons": {
     "clearReset": "Reset the canvas",
@@ -57,7 +58,8 @@
     "zoomIn": "Zoom in",
     "zoomOut": "Zoom out",
     "menu": "Menu",
-    "done": "Done"
+    "done": "Done",
+    "edit": "Edit"
   },
   "alerts": {
     "clearReset": "This will clear the whole canvas. Are you sure?",