P.a. to 50e131244a which solved
https://todo.sr.ht/~emersion/alps/100

Closes: https://todo.sr.ht/~emersion/alps/102

This causes the mailbox to automatically reload the page every 60
seconds, without JavaScript.

This also updates the base template data to include the full URL, and
replaces the earlier "Path" field with a pre-split array of path
components, which is more immediately useful to most templates given the
limitations of string munging with text/template primitives.

Only inline forwarding is supported for now.

References: https://todo.sr.ht/~sircmpwn/koushin/37

Loading remote resources by default has privacy implications.

A new minimal CardDAV plugin is introduced. It injects a list of e-mail
addresses in the e-mail compose view.

References: https://todo.sr.ht/~sircmpwn/koushin/7

Now that all templates are provided by plugins, there's no need to have
a public/ directory. Themes can be in /themes instead of /public/themes.