Sample app: subscriptions over configuration change

[tomhermann]

Currently when a view is paused, takeView() is invoked, which disposes the subscription. It would be better if the progress continued.

Perhaps instead of long lived presenters or singleton models, consider something better.

It should:

• Generally: Continue running on configuration change, stop running when destroyed.
• Bonus pts: Configure when the subscription should be disposed: if it is a destructive server operation, keep on going. If it is just a view subscription, kill it when you feel like it.
• Bonus pts: Consider using a Lifecycle observer