Standardise avatars used with other properties

[abridger]

• Loads avatars from user object, or falls back to default avatar, as with all other properties
• Ensures that there are no discrepancies between development/staging/production
• Also ensures that the kano-nav won't be displayed on the kit

Trello card: https://trello.com/c/pk2YZCef/1716-make-art-user-icon-broken