Avatars make blame page slow

Summary

Esp with a page with many commits listed, avatars slow down the rendering of the blame page significantly.

Steps to reproduce

I see this running GitLab with GDK and doing a blame of a file from the Linux OS source code. There appear to be many queries

Actual behavior

(What actually happens)

Relevant logs and/or screenshots

Possible fixes

I'm currently working on an attempt to use a single query for loading all of the users, and I also want to take a look a caching the icons.