Make Port calculatePosition faster

[bergie]

Currently position calculations seem kind of heavy. On a graph with 45 nodes that contain 105 ports, the calculation can take around 500-700ms.

A big part of this might be the fact that each port queries its siblings to find its relative position. It might be better to put the-graph-inports and the-graph-outports into the driver's seat to make this more coordinated.

See gss/gss#6