NLA track drag-and-drop re-ordering

It is not currently possible to re-order NLA tracks by simply dragging and dropping. There is only a sad little context menu where you can move the track up and down by single increments.

When a scene has lots of NLA tracks, reordering these things are truly a pain.

The user should be able to drag-and-drop NLA tracks similar to how drag and drop works in other parts of the interface (e.g., panels).