miscellaneous fixes

Summary

This merge request:

• increases HSTS timeout value to 1 year
• implements Marianne's request for peak heat load to have another decimal place
• stops deleting a scenario from breaking the scenario chain (#1014 (closed))
• sorts heating times table entries to avoid accidental breakage (#1011 (closed))
• adds the ability to assign assessments to organisations (#1002 (closed))
• adds a graphic for baseline on the commentary page, per Gervase's request
• add featured image data server-side so there's always a current URL (#1005 (closed)); requires yet-unmade changes to report template to be useful

Checklist

• Documentation impact considered
• Manual smoke test run (if possible)
• Local-only tests run
• Assigned related ticket to reviewer