Add volume dialog icons specific for tv

We add 3 new volume icons - when tv is muted, when the volume is low and
when it is high. The threshold between low and high is 12 (i.e. maxVolume / 2).

We introduce a new config - config_show_low_media_volume_icon. By
default this is disabled. Only for tv it is enabled. The low volume icon
for non-tv devices is the same as the normal media volume icon
(ic_volume_media). Therefore, if the config is enabled on a non-tv
device, there would be no visible change.

Test: m && flash && check new icons are in place
Change-Id: I07ffc24312a5aa59dc491f967042d4cb3685e101