python: allow loading of multiple robots

RobotLoader

Remove lights from Anymal robot

python: fix double negative

[Talos] fix collision shape of the ankle

Fix Hyq srdf (disable collision pairs)

And activate tests again

add talos full

to avoid a dependency to https://github.com/stack-of-tasks/talos-data/
in many packages

[Python] add more paths to getModelPath, fix #37

and document their purpose

 [Python] add a load helper, and use it in main & tests

Which lead to find that double pendulum, hector and iris were not
tested.

Writing a test for hector raise:
> IOError: hector_description/robots/quadroto_base.urdf not found

Which lead to find that __main__ was missing the variations of icub &
ur5

Gathering all expected available robots and parameters in one dict
indexed by names avoid the need to duplicate those informations.

In the previous version, changing NQ / NV, wouldn't change the test
results.

Also, we had a test checking that talos arm had a free flyer,
and another test checking that talos arm didn't had a free flyer.
Both were passing.

[Python] Add (and use) a robot_loader function