[FEATURE] Add scroll bar option

**Is your feature request related to a problem? Please describe.**
Navigating large diagrams is hard currently. Also the horizontal scroll is broken for me.

**Describe the solution you'd like**
Please add an option to toggle scroll bars on the diagram view.

**Additional context**
n/a

Start by locating the diagram view and inspecting how its current horizontal scrolling is implemented. Add a user-controllable scrollbar option without regressing horizontal navigation; done means the option visibly toggles scrollbars and large diagrams remain navigable.

Written by the indexing model from the issue text.