Added infection and visibility features. Tested them. They work.

Visibility and infection features are added and tested.
Could you also have tests that check for a cell's visibility being set both positively and negatively when they should be (by which I mean, test a case where that cell is visible, test a case where a cell is not visible, and make sure it is right on both). Same for infection.

It's also worth noting that these tests might be modified as I implement the visibility across the grid Model, since like the computer will be visible and it's neighbors and everything it is connected to. I'd appreciate a comment alluding to that.