Dependency updates

- Adding topojson to readme
- Updating express dependency to match documentation
DB error handling

- Check DB connection at app startup, fail if invalid
- Log query errors
Logging, DB queries, HTTP response

- If the HTTP response data is empty, don't sent a content type as this
confuses Firefox. Return a 204 with no content-type instead.
- Handle DB connection error once application is running
- Split DB query onto multiple lines for readability