Select notes by dragging

[Kangaroux]

The user should be able to drag their cursor to select a group of notes. If the user is holding down shift or control, whatever is selected should be added to the current selection

If the user starts dragging and scrolls the notefield the selection box should grow/shrink accordingly. In other words, when the user starts dragging, the point they clicked at should be relative to the notefield's current scroll position.