Reintroduce Firewall GTK+ Applet

Current Firewall Applet - Qt5 based, has too many unnecessary dependencies. For those using GTK+ based Desktop Environments there is a very elegant solution, reintroduction of the Firewall GTK+ Applet. Not only that GKT+ based Applet works just as well as its Qt5 counterpart, but it also provides genuine GTK+ Look and Feel within modern GTK+ Desktop. Ref. https://bugzilla.redhat.com/show_bug.cgi?id=1404328