Implement online offset calibration for a subset of FT sensors

In many cases it may happen that some FT sensors can be offset-calibrated, while other no, and it would be convenient to just calibrate them. For example, when a humanoid robot is standing on its leg, the FT sensors on the legs cannot be offset-calibrated, while the one on the arms yes (assuming no force is excerted on the arms).

For a specific application, I implemented an hardcoded implementation of this in https://github.com/robotology/whole-body-estimators/commit/ac0cd227b67aee4fa2170148970e2752cf38bd7c . However, it would be good to have a model agnostic implementation. Possible way of implementing this:

O1: Define in the config file "groups" of FT sensors, and then this groups can be used as the calib_code in the RPC calls to calib*** RPC calls (see https://github.com/robotology/whole-body-estimators/blob/c46c1852974776038a75b7c0e542ccb2917d7c7f/idl/wholeBodyDynamics_IDLServer/wholeBodyDynamics_IDLServer.thrift#L18).
O2: Define new calib** functions (or at least for calib, as all other calibration methods are not really relevant for the arms use case) in which the list of sensors to calibrate is explicitly passed when the RPC function is called.

In general I would prefer O1, even if it has the downside to put even more complexity in the configuration files that it is definetly something not desirable, so from that point of view O2 has the advantage that we would not need to put more complexity in the config files.

robotology / whole-body-estimators

Implement online offset calibration for a subset of FT sensors #164