Fix issue with DisplayObject.skewY being assigned to the prototype.

Signed-off-by: Grant Skinner <info@gskinner.com>
Update DisplayObject.clone()

Signed-off-by: Grant Skinner <info@gskinner.com>
Renamed cloneProps to _cloneProps.

Follow protected method naming convention.

Signed-off-by: Grant Skinner <info@gskinner.com>
Added Container._cloneChildren()

Signed-off-by: Grant Skinner <info@gskinner.com>
Updates to .clone()

Fixed _cloneProps name in docs. Simplified logic.

Signed-off-by: Grant Skinner <info@gskinner.com>