Zulip Server 1.8.1

• Added an automated tool (manage.py register_server) to sign up for
  the mobile push notifications service.
• Improved rendering of block quotes in mobile push notifications.
• Improved some installer error messages.
• Fixed several minor bugs with the new Slack import feature.
• Fixed several visual bugs with the new compose input pills.
• Fixed several minor visual bugs with night mode.
• Fixed bug with visual clipping of "g" in the left sidebar.
• Fixed an issue with the LDAP backend users' Organization Unit (OU)
  being cached, resulting in trouble logging in after a user was moved
  between OUs.
• Fixed a couple subtle bugs with muting.