First draft implementation of pervertex normals for quantized-mesh.  Will need to update other meshes that use the CentralBody shaders.
Added new request headers to that specifies the content type as quantized-mesh or a quantized-mesh with vertex normals.  Added flags to CesiumTerrainProvider that specify (1) should the client request vertex normals and (2) does the server have vertex normals.
Minor cleanup.
If no vertex normals are in the mesh, then do not add junk normal data to the vertex buffer.  Fixed Globe shader so that day-night shading can be used again.
Updated hasWaterMask and hasVertexNormals to be properties.
Added unit test to load QuantizedMeshTerrainData with VertexNormals.
Added unit test to test rendering of quantized-mesh terrain with lighting enabled.
Merge remote-tracking branch 'agi/master' into quantizedmeshVertexNormals
Merge remote-tracking branch 'agi/master' into quantizedmeshVertexNormals
Moved calculation of normal eye coordinates over to the vertex shader (in the case of pervertex lighting).
Added unit tests for new builtin functions.
Updated CesiumTerrainProvider.requestVertexNormals documentation, fixed copy/paste bug in GlobeVS.glsl
Removed local data type byte length in favor of using TypedArrays.BYTES_PER_ELEMENT
Added private QuantizedMeshExtensionFlags enum and cleaned up test for the octencoded vertex normals extension.
Merge remote-tracking branch 'agi/master' into quantizedmeshVertexNormals

Conflicts:
	Source/Scene/Globe.js
	Source/Shaders/GlobeFS.glsl
	Specs/Scene/TileSpec.js
Updated Changes.MD.  Globe.js change was supposed to be in the last commit.  This was a change that resulted from the last merge from master.
Updated CHANGES.md. Minor cleanup.
CesiumTerrainProvider.requestVertexNormals is now readonly.
Minor doc updates.
Added an example that demonstrates the use of the per-vertex normals for the CesiumTerrainProvider.