CSL styles-distribution updater

This is a WSGI app to update the CSL styles distribution repo based on a Travis CI webhook defined in the main CSL styles repo.

Example usage:

cd scripts
gunicorn -t 3600 -b 127.0.0.1:8080 --env AUTHORIZATION=[webhook-token] --access-logfile - webapp

The WSGI server should be run as the user defined in the bin/update_permissions script, which can be used to properly set permissions on the styles submodules.