trainPart referencing an itinerary (de: Zugteile referenzieren auf den Fahrtweg)

The TT element ocpTT generates heavy redundancies in case of coupled train parts. That may be avoided by "outsourcing" this element into the higher hierarchy and referring to the same "ocpsTT" for coupled train parts.

This new element may be called itineraries with proper itinerary child elements that work like the current ocpsTT grouping together with an id attribute.

<timetable>
  <timetablePeriods...>
  <operatingPeriods...>
  <categories...>
  <annotations...>
  <itineraries>
    <itinerary id="it1">
      <ocpTT ocpRef="d2e275" ocpType="stop">
        <times scope="published" departure="07:37:00.0" />
      </ocpTT>
      <ocpTT ocpRef="d2e277" ocpType="pass">
        <times scope="scheduled" arrival="07:39:54.0" departure="07:39:54.0" />
      </ocpTT>
      ...
    </itinerary>
  </itineraries>
  <trainParts>
    <trainPart id="d2e370" line="41" trainNumber="2109" timetablePeriodRef="d2e330" categoryRef="d2e362">
      <formationTT formationRef="d2e316" />
      <operatingPeriodRef ref="d2e347" />
      <itineraryRef ref="it1" />
    </trainPart>
  </trainParts>
  <trains...>
  <trainGroups...>
  <rosterings...>
</timetable>

Mentioned in: http://www.railml.org/forum/ro/index.php?group=2&id=399