Update the test for updating a talk node as it was essentially doing the
same as the test for creating a new talk node.
The test now ensures that the talk is saved before adding an event, and
that the talk created date is different to the original created date as
well as that it matches the latest event date.
To ensure that the event dates for a talk are always in the correct
order, and to make the editing experience easier, this change
automatically re-orders the events on a talk node to be based on the
event date.
Fixes#74
Automatically update the created dates for talk nodes so that they match
the most-future event. This means that the talks are ordered correctly
on the Talks page.
