Client: default to empty cache
Fix: genre DTO additional key
client.py: use direct classes for mapping
Move BO classes to their own file
Move mappers to their own file
Move transports (and config) to their own file
Safer `None` test
Forget `use_cache` TODO
Use more precise cache methods
`fetch_playlist_url` -> `get_episode_playlist_url`
client.py: Remove unimplemented `search_terms_max`
`search_terms` -> `search`
Follow English order for class names
Forgot some files...
Client: use Requests instead of urllib