Switch the ActiveJob backend from DelayedJob to GoodJob. Differences:
* The job worker is run with `bin/good_job start` instead of `bin/delayed_job`.
* Jobs have an 8 hour timeout instead of a 4 hour timeout.
* Jobs don't automatically retry on failure.
* Finishing jobs are preserved and pruned after 7 days.
* Listen on port 3000 instead of port 80. Port 80 is prone to conflicts
with other webservers.
* Use the production version of the Danbooru Docker image. It's less
likely to have bugs than master.
* Fix the autoinstall script to work with `curl ... | sh`.
* Lower PUMA_WORKERS to 1 to reduce memory usage.
Fix docker-compose sometimes failing to restart the app. Puma's pidfile
was stored in /tmp, which was persisted across restarts, which caused
restarts to fail because the pidfile already existed. The fix is to
mount /tmp as a tmpfs.
