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

[YesImAsh]

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 (Maybe add a write line to indicate every Bar)

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.

[musikBear]

Please search the issue tracker for existing feature requests before submitting your own. Scrolling play-head in beat-editor is #1195

[DomClark]

1195 refers to the playhead. This issue is about having a scrollbar in the B+B editor, so we don't have to scale the editor to make it all fit in the subwindow at once.