SystemUI: Add config to disable HumanInteractionClassifier

On some devices HumaInteractionClassifier is more of a nuisance than a
useful feature by making the screen hard to unlock at random. Add a
config that allows to define the default state of HIC, which currently
can only be disabled running the following command:

  settings put global HIC_enable 0

Change-Id: I3ad85aff08fe209a21f1eae8a8719c089ed7aa28