Don't make right click popup modal

Making this popup modal is quite intrusive and not consistent with
other popups in KDE apps.


(cherry picked from commit 09e92cfd)

src/main.qml

@@ -195,7 +195,6 @@ Kirigami.ApplicationWindow {
             },
             Menu {
                 id: globalContextMenu
-                modal: true
 
                 MenuItem { action: editPagesAction }
                 MenuItem { action: ghnsAction }