Add PolylineGlowMaterialProperty

This allows for DynamicScnee materials to make use of the PolylineGlow type.

Note, CZML does not support this material yet.
First cut of a general quadtree primitive.
Much better handling of async geometry.
Closer to working ExtentTileProvider in 2D/CV.
Merge remote-tracking branch 'origin/master' into polylineGlow

Conflicts:
	CHANGES.md
Do not release terrain mesh data after creating vertex array.
Add ray-triangle intersection test.
Add ray-triangle intersection tests.
Add ray-sphere intersection test.
Pick rendered tiles bounding spheres.
Pick terrain mesh.
Merge branch 'master' into pick-terrain
Updates after merge.
Merge branch 'master' into pick-terrain
WIP PerformanceWatchdog.
Merge remote-tracking branch 'origin/master' into performanceMonitorWidget
Merge branch 'widgetAndViewerImprovements' into performanceMonitorWidget

Conflicts:
	Source/Widgets/CesiumWidget/CesiumWidget.js
	Source/Widgets/Viewer/Viewer.js
Fix bad merge.
Mostly-working watchdog widget.
Hide the message when the framerate improves.