Now we get decent visual indication of sync errors, for instance. Still
work to do to coalesce alerts so that the screen doesn’t fill up with
them after an interval. And probably we should add a button to clear
all alerts.
Templates for TiddlyWeb URLs are defined in the tiddler
`$:/config/tiddlyweb/host` as a string that can include `$protocol$`
and `$host$`. The default is `$protocol$//$host$/`