SystemUI: Add tunables for clock AM/PM style

Squashed with the relevant fix of:

Author: dianlujitao <dianlujitao@lineageos.org>
Date:   Thu Nov 15 11:33:20 2018 +0800

    TunerServiceImpl: Blacklist Lineage settings from tuner reset

     * They use the tunable infrastructure but are real user settings and
       shouldn't be reset with tuner settings. Moreover, setting them to
       null would cause a IllegalArgumentException.

    Change-Id: Ie05910efaee867632a3bd2e84625d7735259130e

Change-Id: I7f27f135ae0d1e731c936792f655c115f107d20c