Why is AnimationViewModel setting shouldAnimate in the _canAnimate getter?

https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Source/Widgets/Animation/AnimationViewModel.js#L233

This is a weird side-effect and caused some unexpected behavior in another app where we weren't using the animation widget directly.

Start by reading Source/Widgets/Animation/AnimationViewModel.js around line 233, then trace the _canAnimate getter and its callers to understand the side effect. Done means the getter no longer causes unexpected state changes for applications that do not use the animation widget, with the existing animation behavior preserved.

Written by the indexing model from the issue text.