inspector: Clean up includes

Don't include gtk.h, instead include individual headers.
And include config.h and gi18n-lib.h everywhere.

gtk/inspector/classes-list.c

@@ -22,8 +22,16 @@
 
 #include "config.h"
 #include <glib/gi18n-lib.h>
+
 #include "classes-list.h"
 
+#include "gtkliststore.h"
+#include "gtktreeview.h"
+#include "gtkcellrenderertoggle.h"
+#include "gtkbutton.h"
+#include "gtkdialog.h"
+#include "gtkstylecontext.h"
+
 enum
 {
   COLUMN_ENABLED,