Updated CHANGES.md for b13
Add stub for next month's b14 release to CHANGES.md
Produce a built version of CesiumViewerWidget.

The "Cesium Viewer" application is not what people should be using in their own "applications" (simple though those applications may be) that want to use the widget.  So, create a built layer for the CesiumViewerWidget, allowing clients to require that in and recieve all dependencies, allowing them to construct a CesiumViewerWidget instance however they like and put it whereever.
Merge pull request #500 from AnalyticalGraphicsInc/buildWidget

Produce a built version of CesiumViewerWidget.
Merge remote-tracking branch 'origin/master' into terrainRefactoring