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/forum/Gulpfile.js

@@ -11,7 +11,8 @@ gulp({
     '../bower_components/moment/moment.js',
     '../bower_components/bootstrap/dist/js/bootstrap.js',
     '../bower_components/spin.js/spin.js',
-    '../bower_components/spin.js/jquery.spin.js'
+    '../bower_components/spin.js/jquery.spin.js',
+    '../bower_components/fastclick/lib/fastclick.js'
   ],
   moduleFiles: [
     'src/**/*.js',