ImmutableOptimizations should respect react state

[dustingetz]

[dustingetz]

And document it better while we're at it. React ships PureRenderMixin which is not a very good mixin because it doesn't default to value comparisons for the rest of our props, leading to incorrectly skip render in common cases as documented.

ImmutableOptimizations is better because it lets us list things to ref-equals check, and everything else will value-equals check. We could also invert this which I dislike, because the simple cases - like passing a small record {id: 10, text: "hi"} - should work by default. Opt in to the optimizations.