Show user info on annotations

[rgrp]

Want to show useful user info for each annotation (suggest username with that linking to user home page).

Implementation

1. Changes to js library (or a plugin) to show user info.
2. Big question is where username comes from. At the moment just store user id in user field (a uuid). Could store a human-readable username in Annotation store as well. Downside of this is: a) we duplicate username in two places b) what happens if username changes. However as short-term solution it seems the most attractive (only real other option is to have a separate user info API as part of OS ...)