Production deploy: Fetch and display sign database from S3 location

[joshmcarthur]

This pull request deploys:

• NZSL-164: Display the dictionary database version in the application footer
• NZSL-159: Pull Signbank dictionary database from a public or private S3 bucket

It also deploys NZSL-167, which added support for presigning requests for private sign media, but was then reverted, so that's a net no change.