Changing backend database to PostgresQL

Completion of issue #52 (closed), the backend database has been successfully switched to Postgresql. This was developed and tested on the dev VMs, and then fully tested on the AWS dev and playground instances without any issues, with the updated playground instance being used for a low-latency MDC. The old databases were able to easily migrated using https://github.com/AnatolyUss/FromMySqlToPostgreSql with few issues, the details of which have been documented.