`quaternion.jl` no longer necessary?

[mattsignorelli]

All of the functions I see in quaternions.jl have better optimized / more general equivalents in ReferenceFrameRotations (e.g. rotX should just be angle_to_quat(angle, :X). Should we refactor this file to instead use those?

[DavidSagan]

quaternions.jl was originally started before the use of ReferenceFrameRotations was decided upon so yes it looks like a refactoring is needed.