Mobile Responsive Styles (#580)

* WIP: Responsive styles

* Flip breakpoints, ensure doc doesn't spread

* Add MenuIcon

* Refactor Sidebar to share mobile responsive styles

* Fix accidental find/replace

* Tweak padding to take into account icon spacing

app/components/Sidebar/index.js

@@ -1,3 +1,3 @@
 // @flow
-import Sidebar from './Sidebar';
+import Sidebar from './Main';
 export default Sidebar;