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.
1.  Separate with ", " (comma-space) rather than just ",".
2.  Can the badges easily be made links to the pages for those badges (which is where criteria for the award and a list of people who have the badge will be displayed)?