`DateMachine` and `DurationMachine` are only mutated during initialization
and thus do not need shared ownership.
`TitleMachine` is only mutated during initialization and after that only
the callback will keep holding a referrence to it. The `EpisodeWidget`s
get dropped after initialization. So it's justifiable to use `Rc<Mutex<T>>`
instead of `Arc`.
Jordan Petridis
74712b5410