fixed #33: add mugshots to autocomplete. Handle the case where a player
doesn't have a mug yet.
#33: use ng-src so we can use err-src directive as well. Duplicate
ng-src with src for sharing purposes, as we want the URL of the img to
be available to plain old HTTP GETs
fixed #33: move the path to the default-avatar.png image over to
javascript as usemin is cool with it there