fetch_trackers: Make trackers.py self-packaging for Elastic Beanstalk.

This should have no effect on actually running the script, but is useful
if you do want to use Eb or likely some other service like GAE.
fetch_trackers: Use X-Forwarded-For when behind a trusted reverse proxy.
fetch_trackers: Change tracking_domain config to be a full URL.
markdown_souptest: Allow img attributes through.
Revert "Revert "Temporarily use "[deleted]" in JSON for deleted usernames.""