Remove VectorGraphics and VectorVisualizer

See https://groups.google.com/forum/#!topic/cesium-dev/2FpDSXwDvVA
Fixed #1895
Merge remote-tracking branch 'origin/master' into removeVectors
Merge pull request #1896 from AnalyticalGraphicsInc/removeVectors

Remove VectorGraphics and VectorVisualizer
Merge remote-tracking branch 'origin/master' into vertexPositions

Conflicts:
	Source/DataSources/Entity.js