Allow zooming into the curve editor

[HaleyHalcyon]

Acknowledgement

• I have read Getting-Started and FAQ

Description of the new feature / enhancement

I can zoom into the piano roll, but I can't zoom into the pitch editor underneath, which makes it nearly impossible to fine-tune the pitch per note a predefined number of cents.

Proposed technical implementation details

Add the vertical zoom scrollbar to the curve editor as well.