window: Delegate model creation to CcApplication

In order be able to modify panel information statically,
we need to have access to the CcShellModel from static
functions. CcApplication, thus, is a better place for the
model to live, since we can access it outside any scope
using g_application_get_default().

It also makes sense from the modeling point of view, since
the model is not tied to the shell anymore.

shell/cc-window.h

@@ -23,6 +23,7 @@
 
 #include <glib-object.h>
 #include "cc-shell.h"
+#include "cc-shell-model.h"
 
 G_BEGIN_DECLS
 
@@ -30,7 +31,8 @@ G_BEGIN_DECLS
 
 G_DECLARE_FINAL_TYPE (CcWindow, cc_window, CC, WINDOW, GtkApplicationWindow)
 
-CcWindow *cc_window_new (GtkApplication *application);
+CcWindow *cc_window_new (GtkApplication *application,
+                         CcShellModel   *model);
 
 void cc_window_set_search_item (CcWindow *center,
                                 const char *search);