Remove WebGL Globe JSON support and CesiumLanguageConverter

1. WebGL Globe JSON is now supported natively in Cesium.
2. CesiumLanguageConverter is no longer relevant because both KML and WebGL Globe JSON have been removed.
Merge pull request #77 from AnalyticalGraphicsInc/remove-webgl-globe-json

Remove WebGL Globe JSON support and CesiumLanguageConverter
Merge remote-tracking branch 'origin/master' into agi-extensions