Added cortical action for "a = b * c"

This also covers a=b*~c and a=~b*c and a=~b*~c
In merging this, I added a seed to this line (`model = spa.SPA(seed=seed)`) due to some random failures. This doesn't bode well for the robustness of this test, but it's similar to other SPA tests and there's already an issue for making them more robust, so it's good for now.