should make it clearer that this is meant for service disruptions,
not "everything's working fine" announcements.

A simple way to have "announcements" available via API, and otherwise
distinct from the service announcements which show up in Gtfs Realtime.

These are meant to go e.g. be embedded on the operator's website, or in
other places where it's not as easy to display per-trip specific messages.

this does svg templating with hamlet. It might be better to use a
javascript library instead (templating svgs is a little confusing tbh),
but for now i'll see how far i get with this.

This should hopefully be the final (major) part of the restructuring: a
tracker no longer has to know which trip it is on (and indeed it has no
idea for now), instead the server keeps state about which trips are
currently running and will insert incoming pings in a hopefully
reasonable manner, based on their geoposition & time.

There's lots of associated TODO items here (especially there should be
manual overrides for all this logic in the web ui), but that's work for
a future me.

(incidentally, this also adds support for sending all log messages out
via ntfy-sh)

now mostly independent of the gtfs, but still no live-reloading of it.

this is mostly meant to guard against the gtfs changing under
tracktrain, and not yet complete (e.g. a ticket does not yet save its
expected stops, which it probably should).

this is unfortunately uffd-specific, since oauth2 is apparently sort of
a vague standard. But since it doesn't actually do much it should
probably be possible to make it fully configurable & generic if needed.