pickable:false for icons, since we shouldn't assume what they'll be used for
pickable:false for icons, since we shouldn't assume what they'll be used for

Signed-off-by: Chris Malley <74b2712074b149d140079dbd7e875955d192e617@pixelzoom.com>

phetsims/graphing-quadratics,phetsims/graphing-quadratics,phetsims/graphing-quadratics