Add tangent and binormal attributes to BoxGeometry.
Merge branch 'batching' into boxGeometry

Conflicts:
	Apps/CesiumViewer/CesiumViewer.js
Modify tangents and binormals to match the texture coordinate directions.
Add czm_tangentToEyeSpaceMatrix built-in GLSL function.
Add tests.
Add doc.
Update CHANGES.md.
Update doc.
Add default values for undefined vertex attributes.
Merge pull request #772 from AnalyticalGraphicsInc/boxGeometry

BoxGeometry.