Initial support for mobile devices (#787)

* Initial support for mobile devices

No editing yet, but UI looks nice and you can open the canvas menu

* Add support for editing shape color, etc

* Allow the mobile menus to cover the shape selector

* Hopefully fix test error

* Fix touch on canvas

* Fix safe area handling & remove unused Island

public/index.html

@@ -5,7 +5,7 @@
     <title>Excalidraw</title>
     <meta
       name="viewport"
-      content="width=device-width, initial-scale=1, shrink-to-fit=no"
+      content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no, viewport-fit=cover, shrink-to-fit=no"
     />
     <meta name="theme-color" content="#000000" />
     <!-- prettier-ignore -->