Automatic mapping between titles and episodes

[hbredin]

Try to use VTS / TTN fields available in lsdvd output.

• [ ] merge "get_tracks/get_episodes" and update title selection heuristic
• [ ] check existing unit tests
• [ ] add more unit tests for buggy DVDs

[benjisympa]

I don't remember why it's better to merge "get_tracks/get_episodes" but the code is clear like that :

• one step sort track by duration
• one step to re-order by id to have the episode in the final correct order