Load stories in multiple pages

If the scroll is at the bottom, load the next page (if any).

In case of large number of unread stories, this will
- make the first few stories appear faster (feel more responsive)
- lessen the number of stories (and hence DOM elements) on the page
  that will make the page lighter
End of page detection for mobile browsers

jQuery's scrollTop() does not work on mobile browsers

http://blog.jonathanargentiero.com/?p=134