Battery stats: wakeup alarm tracking, general cleanup.

Instead of just tracking the total number of wakeup alarms
per package, track a count for each tag.  Note this is only
wakeup alarms, not non-wakeup alarms.

Also tighten up the code a bit by exposing the actual ArrayMap
container through most of the BatteryStats API, so we can more
efficiently iterate over them (which is all we ever want to do
with those containers at that point).

Finally remove all printing of "since unplugged" stats, as
another step towards completely removing that tracking.  If
nobody screams, hopefully soon we can go through and just get
rid of all the extra state we are carrying around that is
tracking that data.

Also note that currently the per-tag wakeup alarm data is
being reported in the human-readable stats, but in the checkin
data it is still being rolled up into a single number.  To fix
this, I need to completely rework the pkg entry line to have
separate data for services and wakeup alarms (so have three
types -- pkg for the start of a package, wal for a wakeup
alarm, svc for a service).

Change-Id: I8033acca8742935cfe95511cdea730a405b17cab