Settings: enable hex color picker for quicksettings styles

Enable the hidden hex value option in the margaritov color
    picker used in the quicksettings styles menu so users
    can input hex values directly for tile background color,
    tile background pressed color, and text color. This was a
    requested feature.

Change-Id: Ib4e517c38a9edbc1a450c1266daa8b25e1cf4a5f