Add finger_edu robot

cmake

python/example_robot_data/robots_loader.py

robots/finger_edu_description/finger_edu.urdf

robots/finger_edu_description/meshes/base_back.stl

robots/finger_edu_description/meshes/base_front.stl

robots/finger_edu_description/meshes/base_side_left.stl

robots/finger_edu_description/meshes/base_side_right.stl

robots/finger_edu_description/meshes/base_top.stl

robots/finger_edu_description/meshes/frame_wall.stl

robots/finger_edu_description/meshes/lower_link.stl

robots/finger_edu_description/meshes/middle_link.stl

robots/finger_edu_description/meshes/upper_link.stl

robots/finger_edu_description/srdf/finger_edu.srdf

unittest/test_load.py