Mediation exception on assigning both fleet and group to same shape

[jeroens]

The mediation shapes throw exceptions if a shape has both a fleet and a group assigned.

To reproduce:

• Ecosim > Mediation > Apply Mediation
• Assign both a group and a fleet to this shape

The interface allows this

• Now click OK

The mediation shape will assert. Who is right? Let's assess.

[joeb]

It is not asserting any more but we still need to sort out if this is a reasonable thing to do.

[jeroens]

Add informative warning message when trying to apply both fleets and groups to mediation