Implement interface to control PID gain values

[francesco-romano]

We must implement the PID interface (or how it is named in yarp), so the pid gain values are exposed also on the robotMotorGui

@barbalberto

[francesco-romano]

I think this is no longer needed? @traversaro ?

[traversaro]

No, we still need this.

[traversaro]

For implementing IPidControl you have to implement the functions for which we now just have a stub returning false here: https://github.com/robotology/gazebo-yarp-plugins/blob/master/plugins/controlboard/src/ControlBoardDriverPidControl.cpp .

For seeing how the PID gains are loaded at plugin startup (to get an idea how they can be modified on the fly), you can check the setPIDsForGroup method at https://github.com/robotology/gazebo-yarp-plugins/blob/master/plugins/controlboard/src/ControlBoardDriver.cpp#L256.

[traversaro]

If we implement this interfaces, we should check the unit of measurement that we are assuming for the gains (see #119 ).