Improved Note Picking and Support for Sharps/Flats

I improved the note picking: To prevent notes from overlapping the note now follows the mouse position, users can place notes freely wherever they want.

Additionally, I added support for sharp and flat notes, which can be toggled on the left side of the note’s name. It’s a bit quirky as e.g. a sharp F becomes “F#” but a sharp H becomes “C”, not “H#” (thanks music theory!)