Use cloudblue.org subdomains

We should deprecate the use of appspot.com URLs in favor of using cloudblue.org subdomains.

The following subdomains have been created for their respective App Engine projects:

- datablue: data.cloudblue.org
- oceanbench: bench.cloudblue.org
- oceancron: cron.cloudblue.org
- oceantv: tv.cloudblue.org

In addition to the code, we need to replace cron references to

`https://vidgrind.ausocean.org/checkbroadcasts`

with

`https://tv.cloudblue.org/checkbroadcasts`

Search the repository for appspot.com, the four listed project names, and the existing cron URL. Trace each reference to the relevant App Engine or cron configuration and compare it with the requested cloudblue.org subdomain mapping. Done means the deprecated URLs and cron endpoint are replaced consistently and the affected configurations remain valid.

Written by the indexing model from the issue text.