Import Adwaita stylesheet
Install it into /org/gtk/libgtk/themes so that GTK can find it. Make HighContrast and HighContrastInverse into :hc and :hc-dark variants, alias each variant as Adwaita-hc etc themes.
Ensure Adwaita is loaded instead of the default, take care to load Adwaita-hc when HighContrast is selected system-wide.
Use Adwaita-hc-dark as a dark variant of the high contrast mode.
Don't integrate the previous libadwaita styles into the stylesheet yet, that can be done separately and this is a big change as is.
Fixes #91 (closed)