Report time between frames during WebGL playback.
Merge pull request #501 from ScottTodd/between-frames

Report time between frames during WebGL playback.
Fixed phantom scrolling triggered by mouseout.
Merge pull request #502 from ScottTodd/scrolling

Fixed phantom scrolling triggered by mouseout.
Added an experiments system, used with replay frame timing.
Added a skip calls visualizer.

Fixes #499.
Fixed tests, text buttons, cleaned visibility code.
Merge pull request #504 from ScottTodd/experiments

Added an experiments system along with a skip calls visualizer.