Adds three optional arguments for observatory prototype: twotanks (bool), slewMass (float), skMass (float). Adds two outputs to DRM: slewMass, skMass. Twotanks must be true to track the separate tank masses. If twotanks is false, which is the default value, mass decrement from maneuvers only scMass (occulter wetmass)
Fixes #147
Made the requested changes and added testing for TimeKeeper mission_is_over to catch non-positive fuel mass. The redundancies in the SurveySimulation were removed after testing and seeing they weren't necessary.
Adds three optional arguments for observatory prototype: twotanks (bool), slewMass (float), skMass (float). Adds two outputs to DRM: slewMass, skMass. Twotanks must be true to track the separate tank masses. If twotanks is false, which is the default value, mass decrement from maneuvers only scMass (occulter wetmass) Fixes #147