TapQueue server and station 0.18.0

Added

• Startup settings in the console. The settings that could only be changed by editing
  server.toml on the server can now be changed by a full admin on the Server page: client
  sign-in (auth.mode), HTTPS and IPPS (tls.listen, tls.require, the certificate files and
  names), discovery, reverse proxies, and where backups are copied and their passphrase. A change
  is checked first (a certificate file is loaded, a new port tried, and switching to tokens is
  refused while nobody could sign in to the console), kept in the database, and used from the
  next restart, which the page offers; until then it shows both what's running and what's saved.
  What's saved there wins over server.toml; a setting nobody changed keeps following the file.
  server.listen, server.data_dir and admin.token stay in the file only. If a saved setting
  keeps the server from starting, tapqueue-server --forget-console-settings goes back to the
  file. GET and PATCH /api/v1/admin/server/startup. See
  docs/install-server.md.