Fix for some bits of markup that were missing from the output

In the current version, the markup that is defined as $template_body_feed_start and $template_body_feed_end is not included in the output. This isn't visible, but it's the container element for Freetile, so it prevents Freetile.js from working.

This diff inserts the markup before and after the $template_body_feed_item section.

As a little bonus, I implemented Prev/Next browsing with the left and right arrow keys (when the modal window is open). We can add visual clickable arrows at a later step, but most importantly, it's working!