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.
"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).