Added generic data and load functionality for _CZMLBaseObject
Added new modules to czml/__init__.py.
Added the ability to set doc strings on class_properties
Reverted handling of timezones to the proper functionality.  Date/time values with timezones will fail with the current version of Cesium.  A patch has been submitted as pull request #768 in AnalyticalGraphicsInc/cesium.    https://github.com/AnalyticalGraphicsInc/cesium/pull/768