Novoda contributions

Novoda had an internal repo that we were working against for some of our projects and planned on releasing soon but it looks more like something that should sit in RxAndroid itself so here is a PR with what we came up with.

Working with RxJava we realised that, depending on the project, different approaches were possible.
When the project can't use the traditional data layer approach with a UI that subscribes to an observable provided by that layer (UI driven by remote API). We encountered a need for tracking the response to a specific observable from an activity over rotation.

Thus here is tooling to help make that possible on Android:

 - ResumableSubscriber (looking for a better name since it is not a subscriber in the observer sense but performs the act of subscription), allows Loader like tracking over rotation

This is not useful for all architectures but it allows for some interesting usage:
 - defining a ReactiveDialog that allows for mapping actions after user interaction
 - reacting on ActivityResult in a simpler way

I'm not sure about conventions in this project and general direction so let's discuss this and make it happen.