Monochrome colored icons don't work well on a dark background, so now we can
add a border around them. Note that most icons in the interface will remain
without a border, just the outliner and properties editor navigation have
colored icons and those will get a border. Other icons continue to be drawn
in the text colored without a border.
Differential Revision: https://developer.blender.org/D4787
5f7eebda23