Make space-efficient port labels default

[le-cds]

When placing port labels outside, the SPACE_EFFICIENT_PORT_LABELS option causes the labels of outermost north and south ports to be placed "outside of the port area", if that makes sense. This should actually be the default, since it improves graphic association and allows nodes to be smaller. It should thus be replaced by a new option, CONSISTENT_PORT_LABELS, which causes all port labels of north and south ports to be placed to the right of their respective ports.