[Scenes] Fix runtime warnings, and consistent behavior between python and xml

[fredroy]

Note that there are warnings about Mass in the same node, because there are as many AdaptiveFFandMass as there are tools.

 Warning:  [Node(InstrumentCombined)] Trying to add a BaseMass ('unnamed' [AdaptiveBeamForceFieldAndMass] 0x55e365ac6680) into the Node '/InstrumentCombined', whereas it already contains one ('CatheterForceField' [AdaptiveBeamForceFieldAndMass] 0x55e36579c810). Only one BaseMass is permitted in a Node. The previous BaseMass is replaced and the behavior is undefined.
Warning:  [Node(InstrumentCombined)] Trying to add a BaseMass ('unnamed' [AdaptiveBeamForceFieldAndMass] 0x55e36593ff40) into the Node '/InstrumentCombined', whereas it already contains one ('GuideForceField' [AdaptiveBeamForceFieldAndMass] 0x55e365ac6680). Only one BaseMass is permitted in a Node. The previous BaseMass is replaced and the behavior is undefined.

I dont know how to fix it 🤔

[alxbilger]

You can create a Node for each AdaptiveBeamForceFieldAndMass. As is, I suspect that the mass is not taken into account properly. Only the last one contributes to the mass. But the force field part of each AdaptiveBeamForceFieldAndMass should be ok.

[epernod]

Issue #182 has been created to investigate