[doc] Improve generate_doc to generate doc from robot python file
[core] Use add_property instead of reinventing it in wheeled_robot

Moreover, it will ease the automatic generation of robot documentation
(#284).
[test] Add regression test for issue #423
[builder] Fix issue #423

Instead of doing the frame change at the append level, do it at the end
in the after_renaming method. In this way, we don't care about the
relative order between translate(), rotate() and append().
[testing] Use properly morse.testing.testing.main
[doc] Fix the documentation related to #423

While here, remove some other outdated comment, like comment about
WheeledRobot and unparent_wheel
[actuator/waypoint] Revert Waypoint

This reverts commit 4754aeb831b7b7fc73012e646ceacd658c7d5304.
"[actuator/waypoint] not active if no new goal"

It is not consistent to test the "active" state in datastream mode.
(it was OK in service mode, though)