Return a requestID from requestAnimationFrame, add cancelAnimationFrame.

This makes our shim match the standard implementation in features.
Fixed typo in documentation
Removed trailing commas from example
Merge pull request #880 from cmorse/master

Some documentation fixes
Fix crash in Viewer

Clicking on a DynamicObject without a position property causes an exception.
This is a regression introduced in the Viewer refactor.
Merge pull request #881 from AnalyticalGraphicsInc/viewer-crash

Fix crash in Viewer
Fix #879

Allow users to specify `options.imageryProvider` rather than `options.selectedImageryProviderViewModel` when the BaseLayerPicker is not being used.
Merge pull request #878 from AnalyticalGraphicsInc/requestAnimationFrame

Return a requestID from requestAnimationFrame, add cancelAnimationFrame.
Merge remote-tracking branch 'agi/master' into d3demo
Changes after review.
Merge pull request #882 from AnalyticalGraphicsInc/issue879

Fix #879
Make the default timeline labels look like the default Animation widget labels.
Set console container to overflow auto so all logged text is visible.
Merge pull request #885 from AnalyticalGraphicsInc/24-hour

Make the default timeline labels look like the default Animation widget labels
Keep overflow-y: scroll
Merge pull request #886 from AnalyticalGraphicsInc/sandcastleConsole

Set console container to overflow auto so all logged text is visible.
Fix #887

Viewer's dataSourceDisplay needs to be updated in onTick (which causes
it to occur after the clock is ticked but before initializeFrame and render
are called.
Merge pull request #888 from AnalyticalGraphicsInc/issue887

Fix #887
Fix crash when morphing from 2D to 3D.
Updates based on review.