Data usage multi-user support.

Switch to storing policy per-user instead of per-app, meaning each
user has control over their own set of apps.  Summarize the usage of
non-current users.  Only allow owner to make changes to overall
network policy.

Hide auto-sync menu when viewing app details.  Search for
MANAGE_NETWORK_USAGE intent across all package names sharing a UID.

Bug: 7121279, 5419594, 6978663
Change-Id: Ia70f04df70d27da27faccb947cd27021c628a41a