Merge branch 'camera-terrain' into use-ray-intersection
Discretize arc of circle into line segments to use for camera-terrain intersection.
Fix intersection when tilting left. Add intersection tests when panning in 3D.
Merge branch 'use-ray-intersection' into pick-terrain

Conflicts:
	Source/Scene/GlobeSurface.js
	Source/Scene/ScreenSpaceCameraController.js