Add/evaluate a choice of tie-breakers to the dancing links algorithm

[RichardMoot]

[RichardMoot]

One possible tie-breaker would be "commit", which, all other things being equal prefers nodes we have already connected (this would avoid back-and-forth between independent choices).

[RichardMoot]

Another possible tie-breaker would prefer the shorted distance between words in the graph (this would require more information to be stored at the atoms). This tie-breaker would be similar to the proof nets and human processing approaches of Johnson and Morrill