Path visualization improvements.

1. Added `DynamicPath.resoltuion` property for setting the maximum step size, in seconds, to take when sampling a position for path visualization.
2. Improved position sampling to take steps more evenly.  For example, previously, if data was at 61 seconds steps, and resolution was 60.0, steaps would be taken at 0, 60 and 61.  Now they will be 0, 30.5 amd 61.
Merge branch 'master' into pathResolution

Conflicts:
	CHANGES.md
Fix bad caching in DynamicPointVisualizer.

We were not only performing a bad color comparison, we were also caching a reference instead of cloning.  This resulted in point textures never being udpated to reflect the underlying DynamicPoint changes.

@shunter this is the issue I was just discussing with you.
Merge pull request #552 from AnalyticalGraphicsInc/fixPoints

Fix bad caching in DynamicPointVisualizer.
Update CHANGES.md

Fix typo.
Merge pull request #547 from AnalyticalGraphicsInc/pathResolution

Path visualization improvements
Address issue #554

1. Make sure `Animation.destroy` unsubscribes from all events it subscribes to in the constructor.
2. `AnimationViewModel` should throw an exception if a `ClockViewModel` instance is not passed in.
Fix casing of "callback".
Merge pull request #556 from AnalyticalGraphicsInc/issue554

Address issue #554
Merge branch 'master' into computeScreenSpacePosition

Conflicts:
	CHANGES.md