Add the missing SIP stub file

Author: wonder-sk

python/gui/layertree/qgslayertreeview.sip

@@ -0,0 +1,9 @@
+
+class QgsLayerTreeView : QTreeView
+{
+%TypeHeaderCode
+#include <qgslayertreeview.h>
+%End
+
+    // this is just a stub
+};