Add terrain picking that goes through the quad tree instead of the list of rendered tiles.
Initial camera collision detection/response with terrain. Only works with zooming and tilting in 3D.
Merge branch 'camera-terrain' into pick-terrain
Merge branch 'camera-terrain' into pick-terrain
Add sphere-plane and circle-circle intersection tests.
Add plane-plane intersection and 2D line-circle intersection.
Merge branch 'camera-terrain' into pick-terrain
Add triangle-circle arc intersection test.
Add terrain arc intersection test.
Some terrain arc intersection fixes.
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
Clean up intersection tests.
Clean up and add doc.
Fix tests.
Update doc and add intersection test specs.
Some fixes after renames and for 2D/CV.
Merge branch 'camera-terrain' into pick-terrain