Separate core CZML from AGI extensions

For now extensions are managed in the same repository but that may change in the future.
Forgot to save sln.
Add an extensionPrefix property to schema

Use it to label extensions as such in the Markdown.
Merge remote-tracking branch 'origin/master' into agi-extensions

Conflicts:
	DotNet/CesiumLanguageWriter/Generated/PacketCesiumWriter.cs
Merge remote-tracking branch 'origin/master' into agi-extensions
Sensor renames

Also modify code generator to not use the extension prefix in class names (we may eventually put them into a namespace).

Also regenerate Java.
Remove nonexistent file.
Merge pull request #78 from AnalyticalGraphicsInc/agi-extensions

Separate core CZML from AGI extensions