Add a "gain" and "loss" transition for sites

[jordansread]

When a new one comes on line, emphasize it (e.g., scale stroke width from 0 to 140% to 100% within ~1 second)

When we lose one, scale down from 100% to 0 (~1 sec?)

This is a bell and whistle feature that would be really powerful, but is not a priority for us right now. It may also bog the browser in the rendering (but we don't know w/o testing).