Basic SpaceCenter functionality

[djungelorm]

See https://github.com/krpc/krpc/blob/main/service/SpaceCenter/src/Services/SpaceCenter.cs

• SpaceCenter.GameMode
• SpaceCenter.ActiveVessel
• SpaceCenter.Vessels
• SpaceCenter.Bodies
• SpaceCenter.UT
• SpaceCenter.G
• SpaceCenter.WarpRate/WarpFactor etc. - these are a bit different in KSP2?