Got rid of all the debug harness and refactored graphstate.py

We fail when running against Anders and Briegel simply because we use a
different CZ table

Think CircuitModel.act_cz is wrong

The mistake was in the set of gates which commute with CZ

But it is not symmetric. I wonder why. Can run with either for now.

Using `combinations` instead of `combinations_with_replacement` was
leading to entries of the form [ ... , i, i] being excluded from the CZ
table.