Adds a new model that implements full state feedback on the linear Carvallo-Whipple model.

[moorepants]

If the steer and roll torque are used to stabilize to the upright equilibrium you can use full state feedback to drive all states to zero. This is a general model that implements this feedback and steering/roll torques can still be applied in parallel from the rider. I demonstrate finding a simple LQR controller for all speeds in the docs:

TODO:

• [ ] Make a new parameter set that includes these control gains (instead of just adding them in the model.
• [ ] Make sure that all the controls are calculated correctly, try some simpler controllers on steer and roll.