Fix #461 move youtube upload into new cli
- Remove src/youtube-uploader
- Refactor YoutubeFrontend to fit new cli
- Refactor YoutubeService to fit new cli workflow
- Add subparsers to cli.py
- Document argument parameters, update docstrings
- Check oauth2 token file exists before upload
- Use positional arguments in cli.py
- Cleanup frontend/youtube.py
- Make methods static where possible