Feature: Hint viewer (#666)

* Add Hint viewer

- Add hints for arrows and lines
- Add hints for resizing elements

* Swap priority of multi mode and resize mode in Hint Viewer

* Remove dangling locales from public

* Add shortcut to hide hints

* Change hint texts and show resize hint ONLY during resizing

* Remove hints toggling

src/locales/en.json

@@ -77,5 +77,10 @@
     "canvasActions": "Canvas actions",
     "selectedShapeActions": "Selected shape actions",
     "shapes": "Shapes"
+  },
+  "hints": {
+    "linearElement": "Click to start multiple points, drag for single line",
+    "linearElementMulti": "Press Escape or Enter to finish",
+    "resize": "You can constraint proportions by holding SHIFT while resizing"
   }
 }