create md-sal models / listener for all types of OFErrorMessage

Currently all error messages produced by OFPlugin are consumed on MD-SAL side by implementation of SalFlowListener.onNodeErrorNotification. But only one type of OFErrorMessage refers to flows. All other error types should be modeled in separated yang so that there will be generated separate listener and corresponding error models, suitable for md-sal to support dispatching of non-flow errors (from OFPlugin) to somewhere else (on MD-SAL side).

If possible, this could be done after models get separated from MD-SAL.