Add package.xml to allow build in catkin workspace

See merge request gepetto/example-robot-data!17

[CMake] use PYTHON_INSTALL_ON_SITE

See merge request gepetto/example-robot-data!16

PYTHON_INSTALL_ON_SITE does the PYTHON_BUILD and the INSTALL, but they
require to have the same arguments. Then, we have to put the CMakeLists
in a parent folder of the module, as `python`, or `bindings/python`.

anymal srdf : add disable_collision for adjacent links

See merge request gepetto/example-robot-data!15

Added ANYmal b (this is now open-source and legally possible)

See merge request gepetto/example-robot-data!14

add ur_description, fix #7

See merge request gepetto/example-robot-data!13

from https://github.com/ros-industrial/universal_robot/tree/kinetic-devel/ur_description

some models don't have robot parameters, fix #13

See merge request gepetto/example-robot-data!12

to comply with other packages

Added solo robot + fixed bug in the unit-test

See merge request !11

to ease robotpkg packaging

s.t. Pinocchio can depend on the data, and we can provide simultaneously
several python versions