Add frame and frameName options to forceTorqueSensors

[traversaro]

The forceTorqueSensors option in the YAML file permits to export the FT sensor information in two ways:

• as a Gazebo-specific extension of URDF, that embeds inside the URDF a snippet of SDF that describe an FT sensor (see https://github.com/robotology/simmechanics-to-urdf/blob/master/simmechanics_to_urdf/firstgen.py#L1874 and http://gazebosim.org/tutorials?tut=force_torque_sensor&cat=sensors)
• as a iDynTree-specific extention of URDF, that embeds inside a URDF a sensor tag with similar semantics to the sensor tag in SDF (see https://github.com/robotology/simmechanics-to-urdf/blob/master/simmechanics_to_urdf/firstgen.py#L1843).

In both those cases, however some parameters that describe the sensor are hardcoded:

• The frame element has been hardcoded to have the child value, while it could also accept the sensor or parent values (see http://gazebosim.org/tutorials?tut=force_torque_sensor&cat=sensors#%3Cframe%3E)
• As the frame element was hardcoded to be child, then the pose element in SDF or origin in URDF, that describe the location of the sensor w.r.t. to the child link frame, was not specified and so default to the identity value. This made sense because this transform is only considered (and only for the orientation part) if the frame tag is equal to sensor .

Due to the specific needs of generation of the new iCub3 model, it could make sense to expose these parameters. In particular, this would permit to have all the frame of a given limb to be all parallel in the 0 configuration, without the need to have a single link (the child link of the FT sensor) to have a different orientation to match the one of the sensor.

@Nicogene @prashanthr05