Update meshcat_visualizer.py by adding set_property

[LudovicaDanovaro]

We changed this script by adding the function to set the "color" property in order to modify the color of a shape (such as a sphere) during the simulation. However it is impossible to change it in the animation

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[GiulioRomualdi]

We tested the PR together. We were not able to make it working for the animation. However, this is something we can investigate later