frameworks/base: Addition of Changes for ZeroBalance feature.

--Addition of code to receive broadcast from ZeroBalanceHelper
  application for executing command to write block/unblock
  rule to Iptable.
--Addition of ZeroBalanceHelper file to be accesible by other
   modules to notify ZeroBalanceHelper application about update
   on change of SIM balance.
--Addition of rule to allow browser uid when rest all applications
  are in blocked state.
--Addition of feature flag to control the zerobalance feature.

Change-Id: Iedfd96855b36778d9d49c567f8f5b1a184633298
CRs-Fixed: 927258