Add per-person award administration and per-event "Assign awards" button

Fixes #37, although see my uncertainty about the "Assign awards" logic
in the "POST /workshops/event/{slug}/award" commit message.
On Sat, Dec 27, 2014 at 02:28:56PM -0800, Greg Wilson wrote:
> > +<form action="{% url 'event_award' event.slug %}" method="post">
> 
> Why the name `event_award`?  Because the award is being made from
> the event page?

Because we're creating the awards triggered by the the event in
question.  Maybe ‘create_awards_for_event’?  But that doesn't follow
the <model-name>_<qualifier> pattern you have going for the other
per-model-instance URLs.