Add toLocation to EconomicEvent
This is to fix the hack when we said we could use event atLocation to update the resource currentLocation when needed. This was part of the tightening up of what could and could not be updated directly on the resource instead of requiring an event. At the time, we didn't want to add a new property. It has become apparent that we should do this correctly.
Feedback welcome.
I still need to update the UML and add it to this MR.