when it was useless otherwise

With trivial factorizations,
to avoid code duplication and ease future robot addition.

While here:
- deprecate `loadTalosLegs()` for the factorized `loadTalos(legs=True)`
- use cleaner `os.path.join()` for file path manipulation instead of
  string concatenation

which is the standard way of using pinocchio, according to its examples
and unittests.

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

* 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>

renamed files

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`.