Added
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- Tests for maneuver handling in CCSDS OPM
- OrbitInfos class for rapid orbit additional informations (velocity, perapside radius, etc.)
- Maneuvers have a optional 'comment' field, allowing to give more information
- Declare a maneuver as a increment of keplerian elements with DeltaCombined
- SOIPropagator for rapid extrapolation through multiple Sphere of Influence

Changed
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- `jpl.get_body()` now returns a Body instance and not an Orbit
- Maneuvers now check themselves for application
- The time resolution of a speaker/listener can be modified per class/instances
- 'lambda' and 'λ' are replaced by the argument of latitude u = ω + ν in the Keplerian Circular form
- A big pass over all comments and documentation regarding English