[Picture-in-Picture] Create new sample that highlights this feature

Currently this repository doesn't have a sample that highlights Picture-in-Picture feature. Since Surface Duo is a dual-screen device, it could be interesting implement a basic sample app that highlights this feature and takes advantage of having two screens side by side. It could be that are some exceptions that can affect the behavior of Picture-in-Picture and cannot be done (e.g. maybe is not possible to move the small picture to the adjacent screen, so this exercise is also a r&d one).

More info: https://developer.android.com/guide/topics/ui/picture-in-picture