Fixed bugs in CueFileLoader.

- All cue files are now loading with full metadata, fixed start
position/end position/length issues, and more.
Player: Refactoring of StreamCallback.

- Split into different methods to make the logic clearer.
- Removed player timer and replaced by asychrounous playlist item
loading with tasks.
- Added locks for loading playlist items and changing playlist indexes.
ConvertAudio: Fixed crash when ToMS has an empty string.