Spark Performance Optimizations

I have changed the core UIComponent so that there are no events dispatched on accessors that aren't being bound to, and I already see a nice performance improvement.

I've noticed too that in just clicking on a Panel, for instance, with a VerticalLayout, it has to run through and relayout all of its children, and do all kinds of unnecessary processing.  Should be a boolean or bitmask that prevents that whole cycle.