Data usage UI fixes; sweeps, combined history.

Fix sweep z-order so that limit are always above inspection range,
and draw shadows behind sweep labels.  Narrower margins for sweeps
with labels; push labels to keep from overlapping.

Generous touch targets on sweeps, and delegate touches to neighboring
sweep if nearer.  Refresh sweep layout during axis zoom, and don't
allow zoom below default minimum.  Let inspection sweeps move beyond
valid data ranges.  Draw less-frequent tick marks when working with
large axis ranges.

Remove Wi-Fi policies but continue showing historical data.  Write
NetworkPolicy if modified during read, and snapshot when async write
requested.

Handle combined UID histories for "Android OS."

Bug: 5191421, 5092579, 5225988, 5221101, 5221065, 5221005, 5150906, 5058025
Change-Id: Id51652e8a10bb90e1345f7a8af01bd70cb8ac677