[Feature Request] Drag-n-drop one note into another to make one of them sub-note

[Pheggas]

There is sub-noting. That's fine and great but i'd like to drag-n-drop note into another to make it a sub-note, also!

Step 1

Step 2

Step 3

[cinwell.li]

When you drag to the top of note 1 and drop it, it will become a sub-note.