Updated GNC Utility Functions and Attitude Estimator

[kylekrol]

Updated GNC Utility Functions and Attitude Estimator

Fixes #159. Fixes #161. Fixes #163.

Summary of changes

• Put in an explicit threshold on how "close" the triad vector pairs can be before an NaNs quaternion is returned (currently set to 1.0 degrees).
• Add asserts to enforce invariants on GNC utility functions.
• Update GNC utility function documentation to comment on NaN handling.
• Add in w_sat as an input to the orbit estimator and remove the finite differencing of the attitude quaternion. We currently are just passing the measured omega through as the "estimate", however, this will get replaced by a full filter in the future.

Ptest Effects

Not applicable at the moment. Although, with this merged, work can commence on this.

Testing

Deferring testing for mex functions and fsw integration.

Constants

No change.

Documentation Evidence

See inline documentation.

[kylekrol]

Oh shoot I'm sorry - this is the wrong branch