#16 Reintroduce code paths for artist avatars

Whether or not an artist avatar is generated depends on (an Artist).hasAvatar, which is now a nonexistent property but used to be set according to the Has Avatar field.

Apparently, the Enable Artist Avatars field no longer had an effect immediately prior to data-restructure - artist.js just checks for hasAvatar without concerning itself with wikiInfo.enableArtistAvatars (or as it was called, wikiInfo.features.artistAvatars). This should be fixed!

Fixed in 3bbeea69c6! I also got rid of the feature toggle altogether (c235939a92) - since you now have to specify Has Avatar: true on individual artist documents, anyway.

(In the past, the feature toggle existed I think partially because it would do a file system stat for every artist - dynamically checking if the avatar existed in the media directory. That's not really ideal, and it sounds like it hasn't been supported anymore for a while(?), preferring Has Avatar instead.)