[BalanceControler] [CtrlManager] Balance controler should generate an emergency stop signal if no solution is found.

[thomasfla]

At the moment, if the balance problem comes to be infeasible, the system is stopped by generating a segfault, so it is impossible to investigate the reason of the stop.

A bool signal should be exposed and connected to ctrl-manager.

Ctrl-manager reads this bolean signal: "emergencyStop"
https://github.com/stack-of-tasks/sot-torque-control/blob/master/include/sot/torque_control/control-manager.hh#L108

As multiple entities could stop the control, we could OR the different emergencyStops to then provide the result to ctrl-manager, or we could add emergencyStop inputs on the go via a dedicated ctrl-manager command.

[flforget]

commit 6e69ca3a allow emergency signal creation on the go in ctrl-manager. If one of these signals if triggered, the control is stopped.

the balanceControler emergency signal is still to be exposed and connected