Planet mass should be generated in gen_plan_params

[dsavransky]

Is your feature request related to a problem? Please describe.
Currently, in PlanetPopulation modules, planet paramters a, e, p, and Rp are generated by calling gen_plan_params, while planet mass is generated by calling gen_mass. This causes issues and requires silly workarounds for populations (i.e., DulzPlavchan) that require planet mass to be based on radius. More importantly, we should always allows for correlation between any or all of these parameters.

Describe the solution you'd like
Planet mass should be added as an output to gen_plan_params, and gen_mass should be eliminated as a separate class method.

Additional context
These are the modules defining/calling gen_mass:

• Prototypes/PlanetPopulation.py
• Prototypes/SimulatedUniverse.py
• Completeness/SubtypeCompleteness.py
• Completeness/BrownCompleteness.py
• PlanetPopulation/KeplerLike1.py
• PlanetPopulation/KnownRVPlanets.py
• PlanetPopulation/KeplerLike2.py

Here are the modules defining/calling gen_plan_params:

• Prototypes/PlanetPopulation.py
• Prototypes/SimulatedUniverse.py
• Completeness/SubtypeCompleteness.py
• Completeness/IntegrationTimeAdjustedCompleteness.py
• Completeness/BrownCompleteness.py
• PlanetPopulation/KeplerLike1.py
• PlanetPopulation/EarthTwinHabZoneSDET.py
• PlanetPopulation/SAG13.py
• PlanetPopulation/Brown2005EarthLike.py
• PlanetPopulation/SolarSystem.py
• PlanetPopulation/EarthTwinHabZone2.py
• PlanetPopulation/EarthTwinHabZone1.py
• PlanetPopulation/KnownRVPlanets.py
• PlanetPopulation/EarthTwinHabZone1SDET.py
• PlanetPopulation/JupiterTwin.py
• PlanetPopulation/AlbedoByRadiusDulzPlavchan.py
• PlanetPopulation/AlbedoByRadius.py
• PlanetPopulation/DulzPlavchan.py
• PlanetPopulation/Guimond2019.py
• SimulatedUniverse/KeplerLikeUniverse.py
• SimulatedUniverse/SolarSystemUniverse.py
• SimulatedUniverse/DulzPlavchanUniverseEarthsOnly.py
• SimulatedUniverse/DulzPlavchanUniverse.py
• SimulatedUniverse/SAG13Universe.py