Add unit tests for database
Fix audio unit tests
Fix file class
Implement PlaySong, Queue and Find
Rename attribute
Add __repr__ and __str__ for DB model
Fix docstrings
Implement add_song_metadata
Implement method for metadata fetching from raw audio file
Implement metadata storing and modifying
Add tests for DatabaseInterface and DB
Fix DB and DatabaseInterface according to tests
Merge remote-tracking branch 'origin/stealthyloner-dev' into dev