started file oembed annotation subclass
JSON serialization seems to start working
added FileOembedAnnotation mock data
added unit tests for geolocation annotation

unit testing of ADNGeolocation
* round trip to JSON and back
* conversion to CLLocation object
* creation from CLLocation object
* setting attributes from CLLocation object on a existing ADNGeolocation object
refactored ADNModelTests helper methods into category

the helper methods for recursive object comparison were refactored from
ADNModelTests into its own category on SenTestCase. This facilitates to
test more special models like annotations were additional functionality
need testing.
adapted GeolocationTests to new category with helper methods
Added test cases for FileOembedAnnotations

* Finished implementation of ADNFileOembedAnnotationTests
* Added tests to ensure the correct output
* TODO: write the parser part, too
Merge pull request #20 from westfeld/extending_annotations

Extending annotations to support fileOembedAnnotations