make sync_data.sh copy the latest restart to /g/data/

[aekiss]

Now that things on on /scratch will be deleted if unread for 100 days, we run the risk of losing vital restart files if they aren't copied somewhere safe, e.g. /g/data/.

I've put a warning in the quick start but it would be much better to make sync_data.sh copy the latest restart to /g/data/.

This should

• have separate SYNCDIRs for outputs and restarts, as we don't want the restarts indexed in the cosima cookbook database
• replace previously-copied restarts on /g/data/ to avoid accumulating too many old restarts

[aekiss]

An improved sync_data.sh would also need to be installed and activated in the control dirs for all existing ongoing runs.