Adds a toolbar with a few useful buttons:

- Enable/Disable auto-scroll. Inspired by Moz###lom's auto-scroll script (https://sleazyfork.org/en/users/927364-moz###lom), but able to handle the recent 500 errors.
- Copy last message. Copies the last message sent by the user, and converts bold and italics back into * and ** markdown, ready for you to instantly send again.
- Remove last message. Removes the last user message.