DownloadProvider: Add transfer speeds in notification

This will show transfer speed in notification when in expanded mode.
For multiple files, the combined speed are displayed.

Screenshot: http://i.imgur.com/xqLRvMo.png

PS1: Initial commit
PS2: clean code
     add missing declarations & import

Change-Id: I801dbe61c7ee59d0c1d14d5851ad6dc3a7678499
DownloadNotifier: Normal notification for singles

This builds upon the previous DownloadNotifier, but changes the notification style
when downloading single files by removing the big view.
See this post for more information:
https://plus.google.com/u/0/+Mart%C3%ADndelRosarioOK/posts/hgGcgsFqyp6

PS2: Fixing dependencies
PS3: Removing tabs/whitespace
PS4: Fix missing speed text after last patchset.
PS5: Restore previous change, fix missing time this time.
PS6: Reformat layout

Change-Id: Iaab38d7e7f9de3d9eb3deb5f061ee646b346c7cc