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 02:32:39PM -0800, Greg Wilson wrote:
> > +    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datepicker/1.3.1/css/datepicker.min.css">
> 
> 1.  Does this stuff belong in this PR?

I think so, because entering dates with a text field seems error-prone
and awkward.  But I'm happy to split it into another commit or
pull-request if you want to consider the change independently.

> 2.  Should we use a configuration variable for `https://maxcdn.bootstrapcdn.com` ?

Meh.  I think we should be using Bower here, and not be using CDNs at
all, but I haven't had time to write that up yet.  Until then, I don't
think it really matters where the JavaScript and CSS libraries come
from.