Module 04, Video 04: State Service
Fixed formatting.
Improving unit tests and error handling.
Add StateServiceMock.
Module 04, Video 05: Delay Service.
Fixed formatting.
Module 04, Video 06: Exercise Document Service.
Fixed formatting.
Add ExerciseDocumentServiceMock.
More logging.
Fix document observer logic.
Module 04, Video 07: Audio Service
Fixed formatting.
Module 04, Video 08: Speech Service
Fixed formatting.
Add AudioServiceMock.
Add SpeechServiceMock.
Improved dispose logic.
Module 04, Video 09: System Notifications Service
Fixed formatting.