Reverted back removation of base_inertia + added tiny inertia in base

With this approach, we could reuse this method without the needed of
using RobotWrapper.

update solo12

[README] document ROS_PACKAGE_PATH use

from https://github.com/open-dynamic-robot-initiative/open_robot_actuator_hardware/tree/master/mechanics/quadruped_robot_8dof_v1/stl_files_for_visualization

[CMake] pinocchio required only for tests, fix #22

Fix package paths in URDFs - resolve issues 9,19

* Added quadcopter Iris from 3DRobotics

* [readme] add hector and iris to the launch command

* [iris] Added reduced version of the STL file

Co-authored-by: PepMS <jmarti@iri.upc.edu>

delete duplicate file

See merge request !32