Add scrolling to the B + B editor to make it easier

### Enhancement Summary

Kind of like the scrolling ability in piano editor, music editor and almost everything, i think you know what it is
It is so the B + B editor doesn't have to get stretched if the user ever decides to add more bars

### Implementation Details / Mockup

Just add the ability to scroll through the B + B editor like every other window. It's simple as that, i think

### Please search the issue tracker for existing feature requests before submitting your own.

- [X] I have searched all existing issues and confirmed that this is not a duplicate.

Start by comparing the B + B editor with the piano editor and music editor, which the issue identifies as examples of scrolling behavior. Locate the B + B editor entry point and determine how its bar area is laid out. Done means users can scroll through additional bars without the editor stretching to accommodate them.

Written by the indexing model from the issue text.