Numerical Time Series

[Ipuch]

following :

• [DO NOT MERGE] multi-threading for external forces #866
• Needed to merge the two PRs here  #867

We could enhance the feature of sending numerical timeseries like external forces or motor noise to send a callback instead of an array, that can interpolate them.

• ease the user interface to automatically interpolate time series from XP data
• give intermediate values (interpolated) in collocation, or intermediate integration steps
• When minimizing time, or time considered as a variable to optimize the area on which you want over, the numerical timeseries might change.