Release 9.1.0

• Implemented error page redirection for issues relating to the sign-in link.
• Added redirection to registration page if the email within the sign-in field does not exist.
• Implemented DMCA takedown requests.
• Converted admin email recipient (for bug reporting + DMCA takedowns) from hardcoded value to environment variable.
• Fixed footer visibility.
• Updated dependencies.
• Minor code refactoring.