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 02:28:05PM -0800, Greg Wilson wrote:
> > +  <input type="submit" value="Assign awards" />
> 
> "Assign badges" instead of "Assign awards" - a badge is a thing that
> is awarded to a person, the 'award' is the internal object
> representing that many-to-many association (with some metadata, like
> the date the award was made).

I think distinguishing between “badges” (the types of badges we
assign) and “awards” (the actual badge↔person assignments) was a
useful distinction worth preserving.  If we want to call the
assignments badges, I'd rather call the types something else
(BadgeType?).  I think having Badge and Award models and refering to
the *latter* as “badges” is going to confuse people.