Observables list inside the analysisTree do not appear in the order defined inside the RML

[jgalan]

This might be a minor issue, but when doing ray-tracing using axionlib it would be convenient that the observables inside the analysis tree are ordered in the same way as they are ordered inside the RML processing chain.

This would make it easier to understand the construction logic of the event processing.

I imagine this is also relevant for other processing chains.

I am a bit surprised they do not appear in sequential order.

The problem can be reproduced with the axionlib example examples/full-ray-tracing/helioscope.rml.