Create a new "old DBs" section on the docs, to keep track of where they are

[luizirber]

Every time we updated the "Prepared DBs" section we removed the old links and added new ones. Maybe create another page and move old links there, instead of removing them?

[ctb]

why keep old links?

[luizirber]

Maybe we don't need the old links, but there is the question of what to do with old DBs. Keep them on S3? Remove them?

[ctb]

Separate but related - an idea that came up in discussion with Jason Stajich, it'd be handy to have a machine-readable (JSON? YAML?) file of available databases, that was kept up to date in some standard location. That way we and others could programmatically check to see what databases are available for download, etc.

[ctb]

ref #1005

[ctb]

fixed in #1581.