Break out text color value from commonly used color.

Too many locations are using text_color_white and this will affect
theme options when it comes to the switch_bar_background color.
We can point to a new value, which points to the current value and
all will be right with the world.

Change-Id: I9b1e67b7ce4f31d1e1203cdb11c630682ceb7ba8
Ticket: CYNGNOS-2124