Add mouse rotate functionality

[DrSensor]

Enter rotate and scale on drag mode when double click.

• Use dblclick event listener on this.$slots.default
• [Bonus] add Multi-touch Rotation

Reference: https://codepen.io/drsensor/pen/Vyjaao

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Possible Implementation

• Resize circle on rotation mode

let r = target.attr('r') + (event.deltaRect.width || event.deltaRect.height)
target.radius(r)