Fix VolumeDialog position and appearance on TVs

Create layout-land-television/volume_dialog.xml layout file that
describes layout for VolumeDialog on TVs. (layout-television does not
work since the orientation dimension seems to have priority over form
factor dimension). The new layout file is a copy of
layout-land/volume_dialog.xml but does not contain ringer and
settings_container.
Also adding volume_dialog_gravity integer value which specifies position
of the volume dialog on the screen. The default position
(values/integer.xml) - RIGHT|CENTER_VERTICAL, TV specific position
(values-television) - BOTTOM|CENTER_HORIZONTAL.

Exempt-From-Owner-Approval: TV Branch
Change-Id: Ie73b59f0b25b6cc9f16e24cfd48d38c401647017
Bug: 146436981
Bug: 146188087
Test: make SystemUI
Test: change volume and see Volume dialog at the bottom & center of the
screen, see it does not have bell and setting icons
(cherry picked from commit 7269e9e32f7a2af5590cbe0ff8673ed8608d58e7)