Add more ways to view states/traces

[emichael]

As discussed in the PLSE lunch a while back, other "views" into traces would be nice.

One nice one to have would be a space-time diagram.

Another nice one would simply be a list of transitions taken, along with the states at those transitions. I basically do this in the testing framework, but having things pretty-printed, collapsible, diffs highlighted, etc. would be nice. TLA+ actually does this fairly well (though, since our model of the system is more specific, we can make things look even nicer).