Validator - validate batch table hierarchy

[lilleyse]

@rms13

Spec: https://github.com/AnalyticalGraphicsInc/3d-tiles/tree/master/TileFormats/BatchTable#batch-table-hierarchy

Sandcastle demo in Cesium: http://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=3D%20Tiles%20Batch%20Table%20Hierarchy.html&label=3D%20Tiles

This is one of the more complicated areas of the 3D Tiles spec, so let me know if you have questions. Also I welcome feedback on the spec writing itself if anything is unclear.

[rms13]

• instancesLength must be equal to sum of length property of all classes
• instances.length for a class must be equal to its length property
• classIds.length must be equal to instancesLength
• parentIds.length must be equal to instancesLength when parentCounts is not defined
• parentCount.length must be equal to instancesLength
• parentIds.length must be equal to sum of parentCount values
• classIds values should be 0-(classes.length- 1)
• parentsIds values should be 0-(instancesLength- 1)
• parentCounts values should be 0-(instancesLength- 1)
• cyclic dependencies not allowed

@lilleyse
Am I missing anything?