A new kernel to handle the specific use case of Argo floats recovery

[gmaze]

This PR brings in a new kernel to handle the specific use case of Argo floats recovery.

With this new kernel it is possible to:

• let the float free drift at the surface after a given number of simulated cycles
• change float parameters after the first cycle (i.e. use 2 sets of parameters)

This kernel will automatically be selected when the free_surface_drift parameter will be found in the FloatConfiguration of the deployment plan. This could be used as follows:

    cfg = FloatConfiguration([6903091, 120])  # Load data from the last cycle of the float to recover
    cfg.add('free_surface_drift', 4)  #

With this configuration, the virtual float will start to free drift at the surface after the 4th simulated cycle.