[COLLECTION]: Expose and document functions #211

Hi all,

This issue is a collection of functions that are not yet exposed (EXP) to Python, or need to be documented (DOC).
Feel free to comment any functions where you feel this is needed or edit this top-level comment directly.
If a function needs small code examples, add them to #238.

tudatpy.astro:

• two_body_dynamics
  • LambertTargeterIzzo (DOC)

tudatpy.data:

• save2txt and save_time_history_to_file are defined as the same function. Select a preferred alias and deprecate the other

tudatpy.dynamics:

• environment

  • RadiationSourceModel (DOC)
  • RadiationPressureTargetModel (EXP, DOC)

• environment_setup

  • create_aerodynamic_coefficient_interface (DOC)
  • add_ground_station (DOC)
  • add_mass_properties_model: should these be deprecated? It seems they were superseeded by add_rigid_body_properties?
  • gravity_field.ring_model (DOC)
  • shape.oblate_spherical_spice (DOC)

• propagation

• propagation_setup

  • simulator.propagation_results.single_arc_results (EXP, DOC)
  • create_body_ephemeris: Clarify what body_name does precisely
  • dependent_variable.received_irradiance_shadow_function Clarify the output. Rename to "shadow_function"?
  • propagator.non_sequential_termination (FIX) Missing end of sentence ("two and effectively constitute By using this function,")

tudatpy.estimation:

• estimation_setup

  • observation.one_way_open_loop_doppler (DOC) Expose functionality around DopplerProperTimeRateSettings base class #37
  • observation.two_way_open_loop_doppler (DOC) Expose functionality around DopplerProperTimeRateSettings base class #37
  • observation.two_way_doppler_instantaneous super-seed two_doppler_instantaneous backwards-compatible (EXP, DOC)
  • observation.add_ancilliary_settings_to_observable (DOC)
  • observation.add_ancilliary_settings_to_observable_for_link_ends (DOC)
  • parameter.periodic_spin_variations (DOC) Document the order of the estimated parameters #234
  • parameter.polar_motion_amplitudes (DOC) Document the order of the estimated parameters #234
  • observation.ConstantObservationBiasSettings (EXP & DOC)
  • observation.ArcWiseConstantObservationBiasSettings (EXP & DOC)
  • observation.add_dependent_variables_to_obs_for_links_end (EXP & DOC)

• estimation

  • ObservationCollection (DOC)
  • ObservationCollectionParser (DOC), including associated factory functions
  • SingleObservationSet (DOC)
  • some entries in CovarianceAnalysisInput, EstimationOutput (DOC)
  • create_single_observation_set/single_observation_set (DOC)
  • create_pseudo_observations_and_models (DOC)