Android: Clean up the DownloadManager queue

[SimonSimCity]

Do we have to clean up the DownloadManager queue? Please test if the system keeps track of all the successfully downloaded files or if it's more like a temporary queue.

14b6769#diff-a27810e87ac4ea1f840fd2e699c41639R87

[SimonSimCity]

On Android, most of the systems I've worked with, have an app called Downloads where all finished downloads are listed, no matter where you stored it.

To remove the downloads your app did from this list, you have to remove it manually after the download has finished. See the example: 12de914

This could be done by the CrossDownloadManager, but I currently think it's better to let the developer decide if he wants to remove it. Most developers, I guess, will do it.