Cesium Version 1.15 Released with Support for glTF 1.0

Cesium announce the release of Cesium 1.15. Highlights include: Support for glTF 1.0 and the KHR_binary_glTF and KHR_materials_common extensions. Also, updated the online model converter to output glTF 1.0; Decreased GPU memory usage in BillboardCollection and LabelCollection by using WebGL instancing; New CZML examples thanks to Tiff Lu and Adam Cole from the University of Pennsylvania.