Interface-level network policy, persist policies.

Define NetworkPolicy as cycle-reset day and warning/limit values, and
set/get through NetworkPolicyManager.  Watch ConnectivityManager for
network connection events, and apply quota rules based on matching
interfaces.  Policy service matches based on strong identity to support
IMSI-specific policy values.

Calculates remaining quota based on current stats recorded since the
last reset cycle day.  Tests to verify edge cases around February.

Persist network and UID policies in XML, and restore on boot.

Change-Id: Id40ba7d6eed6094fbd5e18e6331286c606880d80