Show upcoming talks in chronological order

Update the ordering of the future talks on the talks page so that
upcoming talks are shown in chronological order (soonest first),
followed by past talks in reverse chronological order (most recent
first).

This still uses the `created` date for ordering, which is updated
automatically on saving the node to match the furthest future talk, but
I may want to move that into a custom node property at some point.

Fixes #140

config/default/views.view.talks.yml

@@ -8,6 +8,7 @@ dependencies:
     - system.menu.main
   module:
     - node
+    - opd_talks
     - user
 id: talks
 label: Talks
@@ -141,21 +142,20 @@ display:
             operator_limit_selection: false
             operator_list: {  }
       sorts:
-        created:
-          id: created
+        event_sort:
+          id: event_sort
           table: node_field_data
-          field: created
-          order: DESC
-          entity_type: node
-          entity_field: created
-          plugin_id: date
+          field: event_sort
           relationship: none
           group_type: group
           admin_label: ''
+          order: ASC
           exposed: false
           expose:
             label: ''
           granularity: second
+          entity_type: node
+          plugin_id: event_sort
       title: Talks
       header: {  }
       footer: {  }