Adapt to the new convention on the nodes in a ZXGraph

[inmzhang]

In #349, we have adapted to the new RGB color convention in the SketchUp model. There is still a similar problem left behind with the ZXGraph. However, it's a bit more complicated.

Previously in a ZXGraph, we noted the Z-type nodes as those with "Z boundary on all edges, but X on any pair":

That means when there is a junction, we used the color on the bent side as the type of the node. This notation is valid and used in some paper like http://arxiv.org/abs/1905.08916.

However, if you are familiar with ZX calculus, you may notice the discrepency between the old-style spider convention with this. In ZX calculus, a Z basis init/meas is noted with a dangling X spider and a Z spider supports the parity check of all the X computation basis around it.

Austin fixed this discrepency in the draft paper. Now the definition is as follow:

We should keep this change in mind when making changes to the ZXGraph. This may has some effect on the interop between ZXGraph and BlockGraph if I remember correctly.