Remove all configuration for MySQL and configure PostgreSQL as the main
database.

All *_mysql_* options have been changed to *_db_* options.

Postgres requires the database user to have a password in order to
connect via localhost. The db_admin_password option is used to set the
password of the admin user (usually postgres).

Also mailing to root (which gets forwarded to admin_email) for easier automated sorting

Based on playbook from https://github.com/phred/5minbootstrap