Process a single workload in the background

[Sturm Flut]

There are use cases for apps which sometimes have to perform a single, one-shot task that consumes resources over a prolonged amount of time. Examples:

- Creating a panorama picture is highly popular. The pictures taken with the camera have to be "stitched" together, which can take up to a minute on a reasonably powerful phone.

- Locally transcoding a video before it is uploaded or sent via an instant messenger to save data

- Extracting and transcoding audio from a downloaded video (extremely popular with YouTube music videos)

With our current lifecycle the app has to stay focused and the screen kept on until the task is finished.