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
DownloadNotifier: Standardize play store and browser downloads

Image: http://i.imgur.com/w3VaRUK.png

PS1: Initial commit
PS2: Standardize all things!

Change-Id: I5e6c5def7dae10d714fd180693e95bc61205a57b
[2/2] Add to support pause/resume download

User can manually pause current download and resume to continue download remaining data of the file.
add a progressbar to show download progress. (only legacy View)
add pause/resume/stop/retry into notifications
add remaining time into notifications

PSs: Code cleanup.

Change-Id: I7c2c6043bd6e26c4d4b0c74265f87629967302a0