Pay down technical debt

I think along with an hypothetical version 1.0 (and maybe attracting new users and developers) we could clean/tidy a few other things as well, write some more developer documentation, where to look up how ActivityPub works, write down a few things from the video tour through the codebase as text, write some glossary about the terminology. Do a bit of cleanup work and delete old and unused CSS classes. Suppress the confusing exceptions in the maintenance task and fix the timeouts. Maybe gather stats from Celery and tie it into the admin interface.