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/_includes/talk/events.html.twig

@@ -3,7 +3,7 @@
     <h2>Events</h2>
 
     <ul>
-      {% for event in events|reverse %}
+      {% for event in events %}
         <li>
           {% if event.url %}
             <a href="{{ event.url }}">{{ event.name }}</a>