add functions for #1586
Some styling changes for the BaseLayerPicker.
Silly scrollbar.
Merge branch 'master' into cartesian3
update sandcastle
update CHANGES.md
fix documentation
CesiumWidget and Viewer improvements.
Update CHANGES.md.
Pass the timestamp to the pre- and post-render events.
Merge remote-tracking branch 'origin/master' into style-tweak
Merge pull request #1663 from AnalyticalGraphicsInc/style-tweak

Style changes for BaseLayerPicker
Merge remote-tracking branch 'origin/master' into widgetAndViewerImprovements
Fix geometries without indices
Move render error events to Scene.

Also Viewer no longer has its own render loop, it just uses the one in
`CesiumWidget`.
Remove unnecessary public function.
Use spies instead of custom code.
Factor the render func into a separate func.

This way the try/catch won't disable optimization of the entire function.
Remove redundant assetions.
Improve documentation.