Turned out these were some really bad ideas:
1) mapping mime to file types would need to be duplicated in frontend
and backend
2) even if frontend and backend could share mime type map somehow,
frontend would have problems with including it - ajax and the like
3) it either would be impossible to refer to user avatar by their owner
user names in URLs, or dao layer would need to synchronize avatar
content files when user changes his name
4) presenters still need to decorate urls with /data/ and
/data/thumbnails/100x100
5) managing file extensions of thumbnails would be a real pain since it
partially shares its path names with real content, but under
different mime type
Generally it's best to leave it to Apache to transmit correct mime.
