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This patch enables to load and save irt file with position (a couple of float)
for each model (closes: #42).

This patch introduce a new file format. A couple of float is added in the model
definition after the identifier and before the dynamics name.

The "input-output" unit test is updated.

Re-introduce the sin_time_function in kernel and GUI.
(closes: #39).
Co-authored-by: Yves Nedelec <yves.nedelec@cerema.fr>