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
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: I7a27d19fff994876eee07d4c4d63b2808cc516d3
CRs-Fixed: 536562
Add Download Speeds in notification

This commit adds the ability to show the current total download
speed in the expanded mode. This is applicable to both single
and multi file downloads.

Screenshots:
Multi  - http://i.imgur.com/3t7yAy7.png
Single - http://i.imgur.com/MMqmA22.png

Slim'ed by mnazim

PS
- move strings to slim_strings

Change-Id: I801dbe61c7ee59d0c1d14d5851ad6dc3a7678499