[core] Add a FreeZ property to robot

It will change slightly the behaviour of apply_speed for dynamic robot.
It exists already in waypoint actuator, and will be removed from it
[core] Move apply_speed from actuator to robot

It seems more logic to have it at robot level. It is more symetric with
apply_vw_wheels on wheeled_robot. And it will be soon depends of some
properties of the robot.

Update the different caller
[core] Handle apply_speed properly with robot with free_z and dynamic
[builder] Introduce set_{rigid_body, no_collision} to configure robots
[builder] Make RMax a dynamic robot
[testing] Add a test for velocity control for rmax
[testing] Add an actuator on RMax for NED test so it maintains the robot position
[core] Introduce robot::force_position and use it (orientation, teleportation)

It handles the black dance against {restore,suspend}Physics,
linearVelocity and gravity handling. Guessed from a lot of Blender code
reading
[testing] Add a basic test for submarine robot
[actuator] Fix destination actuator to work in 'velocity' mode
[data] Remove logic from submarine
[data] water-1 is set to 'no-collision'
[builder] Make robot more consistent from a point of view of physics

Make robots 'rigid body' when possible, 'dynamic' otherwise. Remove
physics properties of child when necessary / possible.

Now, all robots must be able to run in 'velocity control', at exception
of:
    - PR2
    - Human
    - Quad2012
[builder] Set by default scene.game_settings.physics_step_sub to 2

In this way, the physics is more realist. In particular, it seems to
help the stabilization of ATRV
[builder] Adjust configuration of segway
[testing] Adjust friction test following physics setting change
[actuators] Switch by default to controltype Velocity

Fix #117 (finally) :D
[actuator] Fix waypoint actuator in velocity mode

While here, improve a bit its behaviour when the robot is near its goal
[testing] Adjust several values to pass tests
[core] Change FreeZ by NoGravity as suggested by Séverin