Convert magnetic field to body axes

The magnetic field needs to be converted to body axes before the torque
from the magnetic torquers can be computed.
Gravity Gradient module

Added a module that computes gravity gradient torques.
Add gravity gradient to DDsatCo example

Add the gravity gradient module.
Corrected error on how to compute the maximum torque

Now the actuators saturation is computed using the actuation levels.
Overhaul of the de-tumbling example

Contributions by Zhou Hao