Remove network access for idle apps

Track apps going in and out of idle in the NetworkPolicyManagerService.
Apply DROP rules in firewall controller if app is to be blacklisted
for network access.

Firewall can now be in whitelist (old) or blacklist mode. When in
blacklist, it allows all by default and we can selectively DENY
some uids.

Track app idle in UsageStats and update periodically.
Track charging/discharging states.

TODO: Check for appidle temporary parole state

Bug: 20066058
Change-Id: Ia65d7544204b3bcb78a517310ef4adcc05aac6fb