wayland menu

[David Craven]

> There is already a dbus protocol for this canonical came up with for
ubuntu/unity and it's got support in several toolkits already. Look into
com.canonical.AppMenu.Registrar (google for it).

After some more research it turns out that kwayland has a custom
wayland appmenu protocol to register the dbusmenu address. With the
wlroots layered protocol it should be possible to write a global menu
implementation outside of the compositor. For this some kind of
wayland globalmenu protocol is needed to forward registered dbusmenu
addresses and notify the global menu of which window has focus.