Remove download notification after preview

Removes download notification from the notification bar after
previewing it. There should be an additional check for download
shown in the notifications after completion to prevent from
situation when ContentObserver is unregistered and the onChange
is never called.

Change-Id: I0914a680f08eb96949b56e08719eb28d2e80ccc9
Open images with content://media/ instead of content://downloads/ URI.

This allows images to be shared directly after opening them with the
DownloadManager.

Change-Id: I65c79923b7aef4c1113e572030c9c7f750b73df0
DownloadProvider: Clear notifications for deleted items

Clear notifications for Deleted items from Download list

Issue: Notifications for deleted items from the Download
list are not getting cleared and thus tapping on such
notifications causes crash (Illegal Argument Exception)

Fix: clear notifications for deleted items by adding them
in the stale list

Change-Id: I74e94ccca7ca79ec421d76023c5c894d9487e185