Improve performance

[qwertie]

Back when I used Update Controls, I loved it, with a couple of exceptions, both performance-related:

1. It doesn't understand lists. A list is handled the same way as a single datum, so if you've got an IndependentList<Foo> and a DependentList<FooViewModel> and you add a single item to the IndependentList, the entire DependentList is recomputed from scratch, as well as anything else that depends on it.
2. It doesn't understand changes that have no effect. Suppose I have a Dependent<int> C that computes the maximum value of two other precedents A and B, and then I decrease the smaller precedent A. In this case C does not change, but anything that depends on C is updated anyway. Not only are the dependents updated, but there is no way to suppress this behavior.

Solving these problems is nontrivial, but I have outlined a solution to problem 2 here that appears like it would work. I wouldn't blame @michaellperry if the solution only goes into the replacement project Assisticant though.