gtk3-based GUI, and anticipating built-in XML viewer breakage.

[HinTak]

Fedora is dropping webkit1 in about a year's time:

https://bugzilla.redhat.com/show_bug.cgi?id=1375784

The impact to FontVal is largely just through the built-in XML viewer. It is webkit1 + gtk2 . The gtk2 dependency is also enforced by mono's winform (i.e. windows-like GUI) implementation. Since there is no webkit2 + gtk2 binding, and not likely (webkit2 seems to be very much gtk3 only), in about a year from now, all the work in making the XML viewer work on linux would be un-done :-(.

This situation is somewhat similar/related to
#20
#29

Having a GTK3-based GUI would also ease integration of Mac OS X's webkit framework.

[HinTak]

It has happened - fedora 27 does not ships webkitgtk (i.e. webkit1 + gtk2).