format_threshold_summary should use storm id

format_threshold_interval should only show information on a single storm.

When flowalert is eventually running automatically on a Linux server, we want to see this threshold summary while the storm is happening, and a final summary after the storm is over. format_threshold_interval should only display the most recent storm if that storm has no endtime. Once the most recent storm has an endtime, then the threshold summary should only be displayed once.