Reactivier Reactive{Collection,Table}ViewSource

Pros:

  * No need to keep recreating new instances whenever your data changes outside the `*SectionInformation.Collection` field.

  * New extension methods remove all boilerplate from most uses of these classes.

  * These classes now really look and feel reactive.

Con:

  * Now we require `IReadOnlyList` of `*SectionInformation` instead of `IEnumerable`.  I can't see where this could be a problem, though.