Flexbox model will replace old xul box as the default display model so
this patch adds support for that in a whole bunch of styles.
A lot of style rules are marked as "Fx < 112 compatibility" rules and
those can be removed when 112 hits release.
This way we can handle maximized windows not having the other drag space
like Firefox does normally. This patch additionally adds window control
width values for Win7 Win8 and linux
