SystemUI: Add reading mode tile

Author: Joey <joey@lineageos.org>
Date:   Wed May 16 17:16:06 2018 +0200

    base: add reading mode tile

    Change-Id: I1c515cbeff0dd5a1fa0c00bc9390a66eb104c7f0
Signed-off-by: Joey <joey@lineageos.org>

Author: Michael Bestas <mkbestas@lineageos.org>
Date:   Sat May 26 00:58:57 2018 +0300

    SystemUI: Fix reading mode tile accessibility strings

    Change-Id: I4f0af56e4947b037e1e2dda79132523d13458818

Author: Paul Keith <javelinanddart@gmail.com>
Date:   Wed Aug 8 18:59:25 2018 +0200

    SystemUI: Update reading mode tile for new API

    Change-Id: I9fbf1b4de30079c987b75e37e52e234fa2f86c5d

Change-Id: I365ee54b2b2adc52d804a5fc1d35690ef5636071