Finish switching to full C++ for the whole-body control part + Error is no longer an attribute of the wbc class

Add C++ functions to FootTrajectoryGeneration for more efficient frame conversion + Control from yaml + Again a few changes for RPY to quaternion conversion

Merge from Devel Croco 14/07/2021

See merge request !2

Choice of MPC with integer + Foot trajectory generator after MPC in case MPC optimizes footsteps + Adapt MPC Crocoddyl with footsteps optimization to the new architecture

Switch all solo12 loading to SoloLoader + architecture to run scenarios from another script + Clean test_4 + New EulerToRotation function