Allow expStop for use in experiment cleanup

[k1o0]

Currently an expStop signal defined in an experiment can't be used to update signals when the experiment is ended remotely. This would be useful for triggering cleanup operations, e.g. events.expStop.map(@cleanup). Here's how it could be implemented:

      % Define an expStop signal so the experimenter can use it
      obj.Events.expStop = net.origin('expStop');
      [...]
      expDefFun(obj.Time, obj.Events, obj.Params, obj.Visual, obj.Inputs,...
          obj.Outputs, obj.Audio);

        obj.Events.expStop = merge(obj.Events.expStop, lastTrialOver);

      [...]

    function quit(obj, immediately)
      % if the experiment was stopped via 'mc' or 'q' key
      stopNode = obj.Events.expStop.Node;
      if isempty(stopNode.CurrValue)
        % sneak in and update node value
        affectedIdxs = submit(obj.Net.Id, stopNode.Inputs(1).Id, true);
        applyNodes(obj.Net.Id, affectedIdxs);
      end

[k1o0]

Initial solution to this: ad52845