ID card backend

[jellybob]

This allows volunteer managers to issue ID cards for volunteers to use
as name badges, which also include a year prefixed ID number for
future use. We'll need something to associate those with users in future
years, this year it's sufficient to look up a user because it maps
directly to their user ID.

Admin users can also issue ID cards for orga, orga leads, and role
specific ID cards for things like photographers.

The print queue is consumed by some (currently unreleased) software
which pulls queued jobs using `PRINTER_KEY` configuration variable to
authenticate, which then pushes those jobs to ID card printers
on site.