Clear buffer in Json and Xml grid editors when resultset data has changed.

Else, the last buffer will populate the popup grid.

Added LResultSetEvent::DataChanged, LResultSet::InformDataChanged,
JsonGridEditorRsEVH::DataChanged and XmlGridEditorRsEVH::DataChanged.

L7/special/LGridXmlCellEditor.h

@@ -109,6 +109,7 @@ private:
     XmlGridEditorRsEVH(LGridXmlCellEditor * owner);
     virtual ~XmlGridEditorRsEVH();
     virtual void AfterAction(LResultSet * caller, ACTIONS action);
+    virtual void DataChanged(LResultSet* caller);
 
     void SetResultSet(LResultSet * caller)
     {