Scissor View that can optimize rendering and/or events

[phronmophobic]

It's common to have container elements like scrollviews that visualize a subset of a collection of data. Currently, scissors views still do most of work needed for layout and events even for elements that are outside the scissor view's bounds. For some regular layouts, it's possible to skip work for non-visible elements.

The idea is to have special layouts that given some bounded size, have a fastpath for returning only the relevant elements that might be needed for layout, drawing, event handling, etc.