WIP: draft of simulated signal that is coupled to sample stage e.g. for mesh demo

I think this goes in the direction of a counter that can be used for a mesh demo as suggested for by @valentin.valls

so far it is a dirty draft, but I can run a mesh like

amesh(roby,-1,1,50,robz,-1,1,20,.1,fluo_signal)

and reproduce the experimental data that is provided to the object