Add an easier way to scroll the pattern view in the Splicing GUI

[abilliontrillionstars]

ideally the mouse's scroll wheel could correlate to scrolling left or right, but I'm not sure how feasible this could be in practice.

Chloe suggested using some sort of scroll bar, which I imagined to have a draggable button not unlike the creative menu:

(the "scrolling spellbooks from within the menu" idea is not included in this issue)