UniversalAdmin 1.6.0

Updates install themselves, the project has a home of its own - and a new
look.

Added

• Automatic updates: a new release (of UniversalAdmin or of an
  installed official extension) is downloaded, checked against its SHA-256
  checksum and installed on the next restart. Only within the same major
  version - a major update waits for /admin update. Switch it off with
  update.auto-download: false. Staff with universaladmin.update.notify
  get a notice on join; the console logs it on every check. See
  docs/user/configuration.md and
  ADR 0024.
• /admin update installs every available update at once - the plugin and
  the extensions, a major update too.
• The proxy plugins (Velocity, BungeeCord) check for updates as well and
  log a notice (update-check.enabled in their config.yml). They never
  download anything.
• Documentation website:
  universaladmin-mc.github.io/UniversalAdmin,
  built from docs/ whenever it changes on main.
• New logos for UniversalAdmin, its extensions and the proxy plugins.
• API 1.5: ExtensionManager#updatesFrom(Plugin, String, String) - an
  extension names the GitHub repository it is released from, and
  UniversalAdmin keeps it up to date too.

Changed

• The project moved to the GitHub organization
  universaladmin-mc. Old links to
  nicki41/UniversalAdmin redirect. JitPack coordinates are now
  com.github.universaladmin-mc.UniversalAdmin.
• The official extensions have repositories of their own
  (Discord,
  Placeholders,
  Voice Chat),
  with their own releases. Their jars are no longer attached to the
  UniversalAdmin release; Modrinth is unchanged.

Fixed

• /admin update picked the first jar of a release - the API javadoc - and
  refused it over the checksum. It now takes the plugin jar by name.
• /admin update reports every plugin on its own line: one whose release
  cannot be fetched (for example an extension without a published release)
  no longer stops the others. A missing release and a used-up GitHub request
  limit are named as such.
• "The details are in the server log" now holds for every internal error an
  action reports - its reason is logged.

What's Changed

• docs: roadmap for automatic updates and extension repositories by @nicki41 in #11
• UniversalAdmin 1.6.0 by @nicki41 in #13

Full Changelog: v1.5.0...v1.6.0