Data source naming

1. Data sources now have a `getName` function so that they can be titled for the user.
2. Added utility `getFilenameFromUri` function which takes a url and returns the last segment; which is then used to determine a defualt name if none is provided to the data source.
3. Hooked up `CzmlDataSource` and `GeoJsonDataSource` to use new functionality.
4. Added `DynamicObject.name` which is a user-readable, non-unique, name for the object (if it has one).
5. Hooked up `CZMLDatasource` to process names from CZML.
6. Added specs for everything, updated CHANGES.