[WholeBodyDynamics] Use <sensor> tags from URDF to get IMU frame transformation instead of using massless links

[prashanthr05]

In general, for sensors, instead of dealing with massless link frames (for eg., in some modified version of IcubGazeboV2_5_plus model.urdf being used here, for head imu there's a frame called imu_frame), I think it's appropriate to deal with where head imu's name is head_imu_acc_1x1 (relating to the head IMU accelerometer).

Mainly because of confusions like the following,

Is root_link_imu_acc the name of IMU in Gazebo model? Is there different name for the Gazebo IMU and real robot IMU?

root_link_imu_acc should be the name of the IMU which is coherent with the external xsens IMU mounted to the bottom of the robot, as it can be seen here.
However, the iCubGenova04 model has a an IMU with the name root_link_ems_acc_eb5 attached to the root_link as well (as seen here ), which is different from the xsens IMU. We must be careful about this and not use one sensor for the other, since the sensor transformation matrices for both are different.

this particular case, we did not generate any additional massless link for the xsens imu which is already a source of error