Add followSurface property to Polyline

Goes along with AnalyticalGraphicsInc/cesium/pull/1897
Merge remote-tracking branch 'origin/master' into follow-surface

Conflicts:
	DotNet/CesiumLanguageWriter/Generated/PolylineCesiumWriter.cs
	Java/CesiumLanguageWriter/translatedSrc/cesiumlanguagewriter/PolylineCesiumWriter.java
	Schema/Polyline.jsonschema
Merge pull request #71 from AnalyticalGraphicsInc/follow-surface

Add followSurface property to Polyline