Mobile Support

Tiny devices may not be very good for writing code, but they are good for reading our examples, or giving someone's link a quick review and making some minor edits. With the new Playground, we've improved the small screen experience by: - Removing menu items which aren't related to code. - Some minor style improvements. - Switch to a single pane editor. This means you can't see the transpiled JS. This should make the experience less painful.