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/LPQResultSet.cpp

@@ -63,6 +63,7 @@ bool LPQResultSet::RunSQL()
             m_initialised = true;
             InformInitialised();
         }
+        InformDataChanged();
         return true;
     }
     else