Add the possibility to generate animation in MeshcatVisualizer

[GiulioRomualdi]

Thanks to this PR it will be possible to generate animation on meshcat and eventually export the static HTML file to add to an external website how is it done in https://sites.google.com/view/dnn-mpc-walking/home-page

This PR does not change the classical usage of the visualizer it only adds a new feature. To enable the functionality the user needs to:

1. load all the meshes in the visualizer as usual
2. call the start_recording_animation function
3. Set the frame associated with the transformation with set_animation_frame
4. Set the transform as usual for all the frames
5. Call publish_animation method

Here an example

from idyntree.visualize import MeshcatVisualizer
import numpy as np

viz = MeshcatVisualizer()
viz.load_sphere(0.5, 'sphere', color=[66/255.0, 133/255.0, 244/255.0])
viz.start_recording_animation()

for i in range(100):
    viz.set_animation_frame(i)
    orientation = np.eye(3)
    position = np.array([np.sin(i / 6.0), 0, 0])
    viz.set_primitive_geometry_transform(position, orientation, 'sphere')

viz.publish_animation()

open("website.html", "w").write(viz.viewer.static_html())