Eliminate internal Presenter wrapper shouldComponentUpdate

[nhunzaker]

shouldComponentUpdate is implemented within a special context "sock" inside of the presenter. This wrapper exists to ensure that React context is properly transferred over when extending Presenters. IE10 or lower doesn't transfer static members for ES6 classes.

The reason I did this was to prevent the view model from recalculating too many times when an app changes. If a parent is going to render anyway, there's no sense in recalculating the model when the presenter's subscription fires. Just do it all in the same render.

This commit removes that shouldComponentUpdate method and re-works the efficiency test to test against the model recalculation, not re-render.

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Fixes #188

[coveralls]

Coverage remained the same at 100.0% when pulling ec6f128 on presenter-state into 220c38e on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 443a03f on presenter-state into 443a03f on master.