Add sensor naming convention

[Nicogene]

As per title

cc @traversaro

[pattacini]

Just minor refinements.

[traversaro]

Just a small caveat @pattacini :

Where link is the name of the part the sensor is attached to (e.g., head), type is the type of sensor (e.g., imu), and nr is a number starting from 0.

I would avoid to use part in this context, as part is typically either head, left_arm, right_arm, torso, etc etc while in this context link is the link (i.e. either head, chest, etc etc). The fact that head is both a link and a part does not help. :D

[pattacini]

Correct!
I'll amend it straight on master.

[pattacini]

See ff2f34a.