Significantly improve mobile UX

Most of #137 done.

- Use FastClick to make everything feel more responsive
- Use transforms for animations to make them silky smooth
- Style the drawer the same as the header to keep things simple
- Revert to fixed composer, but allow it to be minimised
- Add a separate notifications page for mobile so it’s easy to go back
- Add indicator to the menu button when there are unread notifications
- Close the drawer when navigating away
- Make dropdowns/modals scrollable
- Many other mobile tweaks and bug fixes

Didn’t take much care to keep CSS clean, due to #103

js/lib/components/back-button.js

@@ -18,15 +18,14 @@ export default class BackButton extends Component {
       m('button.btn.btn-default.btn-icon.back', {onclick: history.back.bind(history)}, icon('chevron-left icon')),
       pane && pane.active ? m('button.btn.btn-default.btn-icon.pin'+(pane.pinned ? '.active' : ''), {onclick: pane.togglePinned.bind(pane)}, icon('thumb-tack icon')) : '',
     ]) : (this.props.drawer ? [
-      m('button.btn.btn-default.btn-icon.drawer-toggle', {onclick: this.toggleDrawer.bind(this)}, icon('reorder icon'))
+      m('button.btn.btn-default.btn-icon.drawer-toggle', {
+        onclick: app.drawer.toggle.bind(app.drawer),
+        className: app.session.user() && app.session.user().unreadNotificationsCount() ? 'unread-notifications' : ''
+      }, icon('reorder icon'))
     ] : ''));
   }
 
   onload(element, isInitialized, context) {
     context.retain = true;
   }
-
-  toggleDrawer() {
-    $('body').toggleClass('drawer-open');
-  }
 }