Bulk actions and clearer sign-in

• Bulk actions: apply changes to several notifications, issues, or pull requests at once
• Copy issues to multiple repositories at once, with a direct link to each new issue
• Create labels without leaving the issue — a plus chip opens an editor for name and color
• Clearer sign-in: a live login log records every step of the connection check
• Servers requiring authentication for API access now work without misleading errors
• German and English translations tightened for consistency