DSDS: Subscription specific for Mobile data, roaming and usage

1. Provide per subscription based support for both Mobile Data
   and Data roaming options. UI and functionality changes in:
   a. Settings -> Data Usage application
   b. Settings -> Mobile Networks menu

2. Provide per subscription based data usage information. UI and
   functionality changes in Settings -> Data Usage application.
CRs-Fixed: 503932

Change-Id: I8e0088dd5cb3de63f880ef02a9cf125f0d986009