Add weights handling to the binary contingency table module

[tennlee]

Weights handling was deliberately left out of the first implementation of the binary contingency table. This should be revisited, the implementation options discussed, and an implementation provided.

[tennlee]

I think the right thing to do is to multiply the event tables by the weightings. I had a discussion with Nick that this might be reasonable, but we will attend to it after merging the contingency table MR and then reviewing the details.