Implement Coulomb friction compensation if torque control is active

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Follow up of #67 .

The nice thing is that all the machinery of defining and reading configuration files and modifying structure is already implemented, via stictionUp/stiction_up/stiction_up_val and stictionDown/stiction_down/stiction_down_val parameters, see for example:

• https://github.com/robotology/robots-configuration/blob/f3fef4277717ae87d825a9a46d994ccd21fef3ec
• https://github.com/robotology/icub-firmware-shared/blob/2a5ec5ac18223be831f6552acecfbca165c63c30/eth/embobj/plus/comm-v2/icub/EoMotionControl.h#L464

Furthermore, we are already back-compatible by default, as all those parameters are defined to 0 in most configuration files! So we are just left with the fun part:

• Make sure the parameters from the configuration files are propagated down to the motor control board
• Implement the coulomb control law that we prefer (what we tested back in 2015/2016 I think is https://github.com/robotology/icub-firmware-shared/blob/bfa54caf76734483efbd9a9930ce90bf954b0351/eth/embobj/plus/mc/EOpid.c#L335, but probably we can just implement directly a new code)

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fyi @isorrentino @GiulioRomualdi @S-Dafarra @DanielePucci