Statsd test app.

Features:
+ Push baseline config to statsd
+ Have buttons to write events to StatsLog (plug/unplug, screen on/off, wake locks)
+ Dump stats log report, and display it on screen (currently support DurationMetricData display).

Test: manual

Change-Id: Ia58d215d30ed7570c0aa1b0627d3b88f8355d425