[modifiers] pose_noise: separate std_dev for each axis

This makes it possible to specify the noise for each axis separately as
a dict.
If a single value is passed, it is used for all axes.
E.g.:
pose.alter('', 'morse.modifiers.pose_noise.PoseNoiseModifier',
				pos_std={'x':0.01, 'y':0.01, 'z':0.1},
				rot_std=math.radians(1))
or
pose.alter('', 'morse.modifiers.pose_noise.PoseNoiseModifier',
				pos_std={'x':0.01, 'y':0.01, 'z':0.1},
				rot_std={'roll':0.01, 'pitch':0.01, 'yaw':0.05})
[modifiers] imu_noise: dict for separate std_dev on each axis
[core] Add an helper for mathutils.Quaternion

Use it in pose_noise and so allow the correct build of the
documentation.
Try to use default interface whenever possible

When setting a default interface to a robot, and adding a component
that is not declared in builder/data.py, it fails.

This commit tries to use, if it exists, the default method of the datastream mw.

Typical scenario: you develop a new component out-of-tree. You want to
test it/debug it with the socket interface. It may work out-of-the-box
(we still display a warning, though).