healthd: refactor healthd code to split into 'charger' and 'healthd'

This splits healthd code into 2 pieces as described below.

charger - statically linked executable in /sbin
 - responsible for charger-mode UI
 - battery/charger  monitoring in recovery/charger-mode.

healthd - dynamically linked (*mostly*) executable in /system/bin
 - responsible for battery / charger monitoring in Android
 - runs 'batteryproperties' service.

Both currently use libhealthd STATIC HALs. However, this now paves
way for the healthd (android) HAL to be a shared library that can
be trebelized.

   text    data     bss     dec     hex filename
 733356   15312   33864  782532   bf0c4 root/sbin/charger
  55943   10392     192   66527   103df system/bin/healthd
 789299   25704   34056  849059   cf4a3 (TOTALS)

Test: Tested recovery, charge-only and android boot with new binaries
with and without STATIC HAL.

Change-Id: I80f94948dda44d466f172d234b3fcc9064ef2476
Signed-off-by: Sandeep Patil <sspatil@google.com>