[cleanup] Created robots folder and moved the description folders there

CMakeLists.txt

...s/anymal_b_simple_description/meshes/base/anymal_base.dae

...ymal_b_simple_description/meshes/base/base_uv_texture.jpg

...s/anymal_b_simple_description/meshes/foot/anymal_foot.dae

...al_b_simple_description/meshes/foot/carbon_uv_texture.jpg

...s/anymal_b_simple_description/meshes/hip/anymal_hip_l.dae

...s/anymal_b_simple_description/meshes/hip/anymal_hip_r.dae

...ymal_b_simple_description/meshes/shank/anymal_shank_l.dae

...ymal_b_simple_description/meshes/shank/anymal_shank_r.dae

...anymal_b_simple_description/meshes/thigh/anymal_thigh.dae

robots/anymal_b_simple_description/robots/anymal-kinova.urdf

robots/anymal_b_simple_description/robots/anymal.urdf

robots/anymal_b_simple_description/srdf/anymal-kinova.srdf

robots/anymal_b_simple_description/srdf/anymal.srdf

robots/double_pendulum_description/meshes/base_link.stl

robots/double_pendulum_description/meshes/link1.stl

robots/double_pendulum_description/meshes/link2.stl

robots/double_pendulum_description/urdf/double_pendulum.urdf

...ts/hector_description/meshes/quadrotor/quadrotor_base.dae

...ts/hector_description/meshes/quadrotor/quadrotor_base.stl