Test NamedSelections with all different extrudes

[RobPasMue]

Looks like with the new server implementation we might have some problems when creating NamedSelections composed by different kinds of bodies (i.e. extruded by different mechanisms). We should test this thoroughly.

[RobPasMue]

Looks like the first issue has been identified: when creating a NamedSelection with a copied body, this crashes. Seems like copied bodies cannot be assigned to a NamedSelection.

Pinging @jonahrb for server-side investigation