fixes #3827 - ldap avatar support

I know this is one of the most inconsequential things ever.  It pulls the jpegPhoto attribute from LDAP as a user avatar.

Currently store it in the DB... (terrible, I know).  My avatar was absolutely tiny at only 4kb.  I could write to public/avatars/<hash>.jpg too, that's probably more sensible?

Just curious if the idea in principle was something worthwhile... it opens the door to further generalizing avatar setup away from only Gravatar.