Apply efficient EventXmlWriting to Freight/Logistic events

[kt86]

In #3539 a new, faster approach was created to write the events.
I would like to implement this also for the events, we have in the freight contrib.

@rakow Do we then still need the "old" attributes logic, or can we just delete it?

[rakow]

The attributes are used for comparing events and other writers apart from XML. There would be ways to get rid of it, but for now it is still needed.