Improved MoI calculations along the lines suggested in #59.

-VesselState now computes the full 3x3 inertia tensor, and sets VesselState.MoI to be the diagonal components of this 3x3 matrix.
-The effect of each part's inertiaTensor and inertiaTensorRotation is taken into account correctly.

-Also, made a minor fix to the attitude controller, may not have much effect.