Cesium 1.0 to-do

[shunter]

• Require a version property on the document object.
• Remove BC code for pixelOffset
• Remove BC code for Image properties
• Remove extra conjugation in CZML quaternions
• Remove existing vectors/sensors and add AGI extensions which will take their place.

1.0 push

• Add a high-level Document class.
• Write an explicit test case which will generate a CZML sample/gallery document.
• Naming inconsistencies between types (rectangular/cartesian vs cartesian2/cartesian3, etc..)
• Improve generated documentation
• Review and streamline generated writers API
• Does JSON schema have a way to define default values?