Get serialization back

[nim65s]

fix #24, revert #26, and fix it by exporting existing .cs to .xml with pinocchio 2.5.6, and importing them back with 2.6.4.

A script to do that is provided, but it must be incomplete, as, for now, this process failed with:

com_motion_above_feet_REF.xml
platforms_REF.xml
platforms_WB.xml
step_in_place_quasistatic_REF.xml
step_in_place_quasistatic_WB.xml
step_in_place_REF.xml
step_in_place_WB.xml
walk_20cm_quasistatic_COM.xml
walk_20cm_quasistatic_REF.xml
walk_20cm_quasistatic_WB.xml
walk_20cm_REF.xml
walk_20cm_WB.xml

The following ones seems good:

com_motion_above_feet_COM.cs
com_motion_above_feet_WB.cs
platforms.cs
platforms_COM.cs
step_in_place.cs
step_in_place_COM.cs
step_in_place_quasistatic.cs
step_in_place_quasistatic_COM.cs
walk_20cm.cs
walk_20cm_COM.cs
walk_20cm_quasistatic.cs

[nim65s]

NB: this was serialized on Arch, and boost version is too high to open that back on 20.04… I'll have to redo it

[nim65s]

Closed in favor of #31, which is exactly on the same commit, but on another branch.