StatsCompanionService connection to Statsd

Created AnomalyMonitor in statsd, which can monitor statsd's internal
anomaly alarms and register the soonest one with the
StatsCompanionService.

This cl introduces the AnomalyMonitor and allows it to register alarms.
It does not yet allow for the removal of internal alarms.

Test: manually added alarms and ensured they were correctly registered
in StatsCompanionService
Change-Id: Iff324c73751c4f43b1507dc64649b50ac388adef