Remove Resources.proto from project
Fix SpaceCenter.Vessels and .Bodies so they don't return new objects for every call
Update tests
Return cached CelestialBody objects from CelestialBody.Satellites
Implement Node.Orbit
Implement Orbit.NextOrbit and .TimeToSOIChange, add .Radius and .Speed
Add SpaceCenter.G, add spacecenter test
Omit non-vessels
Add tests for CelestialBody.Satellites