Use ReactiveList in conductors

As mentioned in #20, conductors should use a `ReactiveList` to expose its items. Yet, simply replacing `IObservableCollection` with `ReactiveList` would be a breaking change in the API, which is better avoided.

The simplest solution would be to:
 - [x] Create a class deriving from ReactiveList that implements IObservableCollection (solves issue #22),
 - [ ] Use this class in conductors (solves #20),
 - [ ] Expose the ReactiveList or its derived object in the conductors, without breaking the API.