A specialized Event tree list providing random order for concurrent Event notes.
Random order is achieved by computing a random insert position within the
range of simultaneous (concurrent) events. Existing connections between
events are maintained, i.e. a new event-note will never be inserted between
two connected event-notes. Connections are only possible between to
successive concurrent Event notes where one of the notes was inserted by call
of the insertBefore() or the insertAfter() method. Most of the methods
inherited from the super class
EventTreeListare only overwritten to
keep track of the existing connections.