Consistent ordering and formatting for talk events

Use a consistent format for talk events, with the most recent talk at
the top of the list with the rest in a descending order.

This removes the need to use a `reverse` filter in the events partial.

source/_talks/so-what-is-this-drupal-thing.md

@@ -5,7 +5,8 @@ video:
   type: vimeo
   id: '49827006'
 events:
-  - name: unified.diff
+  -
+    name: unified.diff
     location: Cardiff, UK
     url: http://unifieddiff.co.uk
     date: 2012-09-05