Inspector: Fix the probe group tree element's data update animation.

* Use two layers to composite the probe tree element icon and animation.
* Interrupt and restart animations asynchronously so that all data updates cause the animation to restart.
* Use an SVG version of the icon, instead of a -webkit-filter on Plus.svg.
Web Inspector: change probe sidebar details table to match Timeline table style.
Web Inspector: fade old probe samples on page navigation.

* Overhaul the row styles so old samples are faded (on non-replay executions).
* Mark missing samples with linear gradient 'barbershop' hatching.
* Copy the TreeOutline selection gradient style as the default for all DataGrid instances.
Web Inspector: animate probe table rows as they are created/added.
Merge branch 'timelapse' of ssh://github.com/burg/timelapse into timelapse