Should the experiment state be set directly by the view, or only by the model?

[jbphet]

I am in the process of implementing the measurement (flip, reveal) for the coins on the "Coins" screen, and I'm undecided about whether the state of the experiment represented in CoinsExperimentSceneModel.singleCoinExperimentStateProperty and CoinsExperimentSceneModel.multiCoinExperimentStateProperty should be set directly from the controls in the view, or if this should only be changed by the model and the view uses more explicit methods on the model the change the state. I'm going to mark it with a TODO and reconsider it later.