refs #768, allow to clear message form

(also fixed wrong reference to resources and deleted unused blackgui resources)

src/blackgui/components/statusmessageform.h

@@ -48,6 +48,9 @@ namespace BlackGui
             //! Set message
             void setValue(const BlackMisc::CStatusMessage &message);
 
+            //! Clear
+            void clear();
+
             //! Toggle visibility
             void toggleVisibility();