[wayland] Proper metatype for ShellClient

Needs meta type declared and properly used in WaylandServer.

shell_client.h

@@ -156,4 +156,6 @@ private:
 
 }
 
+Q_DECLARE_METATYPE(KWin::ShellClient*)
+
 #endif

wayland_server.h

@@ -133,8 +133,8 @@ public:
     quint32 createWindowId(KWayland::Server::SurfaceInterface *surface);
 
 Q_SIGNALS:
-    void shellClientAdded(ShellClient*);
-    void shellClientRemoved(ShellClient*);
+    void shellClientAdded(KWin::ShellClient*);
+    void shellClientRemoved(KWin::ShellClient*);
 
 private:
     quint16 createClientId(KWayland::Server::ClientConnection *c);