Improve the font options support
Improve the font options support

Instead of just overwriting the default options, merge the per-widget
font options with the defaults.

https://bugzilla.gnome.org/show_bug.cgi?id=751811

jadahl/gtk,alexlarsson/gtk,jigpu/gtk,chergert/gtk,alexlarsson/gtk,jadahl/gtk,Adamovskiy/gtk,jadahl/gtk,Adamovskiy/gtk,grubersjoe/adwaita,jigpu/gtk,Adamovskiy/gtk,alexlarsson/gtk,chergert/gtk,jadahl/gtk,jigpu/gtk,davidgumberg/gtk,Adamovskiy/gtk,davidgumberg/gtk,davidgumberg/gtk,chergert/gtk,grubersjoe/adwaita,chergert/gtk,alexlarsson/gtk,davidgumberg/gtk,chergert/gtk,alexlarsson/gtk,Adamovskiy/gtk,jigpu/gtk,jigpu/gtk,grubersjoe/adwaita,chergert/gtk,jigpu/gtk,chergert/gtk,alexlarsson/gtk,jadahl/gtk,jadahl/gtk,Adamovskiy/gtk,grubersjoe/adwaita,alexlarsson/gtk,alexlarsson/gtk,davidgumberg/gtk,grubersjoe/adwaita,davidgumberg/gtk,chergert/gtk,jadahl/gtk,davidgumberg/gtk,jigpu/gtk,Adamovskiy/gtk,grubersjoe/adwaita,grubersjoe/adwaita,davidgumberg/gtk,Adamovskiy/gtk,jadahl/gtk,grubersjoe/adwaita,jigpu/gtk