Settings: use framework text colors for SwitchBar

 * Use framework text colors for SwitchBar also on
   dark mode to properly display disabled colors.
 * Before the patch, a disabled SwitchBar on dark
   mode would look same as an enabled one.

Signed-off-by: Timi Rautamäki <timi.rautamaki@gmail.com>
Change-Id: Ia2fc5eb3f614d899cb5e519c235f1ea9b86a1527