Defer "changed" methods

The following should be able to be called multiple times, similar to `repaint()`, while deferring and collapsing all calls until the end of the thread:

* `behaviorChanged`
Does one of the following:
* `behaviorShapeChanged`
Recalculates scrollbars, followed by...
* `behaviorStateChanged`
Recalculate rects of visible cells, followed by a call to `repaint()`

Right now the two recalc operations are performed on every call. For this reason we have always tried only to make such calls near end of thread, sometimes omitting calls where logically needed to avoid multiple recalcs but sometimes no doubt incurring multiple recalcs needlessly