Bump properties dialog to Xfce 4.14 API
Since the plugin already depends on the minimum Gtk3 version of Xfce 4.14 we can also bump the minimum version of libxfce4ui and drop the deprecated XfceTitledDialog API.
Since the plugin already depends on the minimum Gtk3 version of Xfce 4.14 we can also bump the minimum version of libxfce4ui and drop the deprecated XfceTitledDialog API.