Make the starship scenario playable

[TheHappyKoala]

• Add a timestep control to allow for time warping when thrust is not being applied to the spacecraft.
• Applying thrust as things stand now applies a constant change in the acceleration of the spacecraft - this should be replaced by a more realistic thrust model based on the rocket equation.
• Try to figure out how to use the lambert solver to generate trajectories for a spacecraft travelling from the Moon to the Earth, for example. Right now this does not work.
• Add more information on the state of the spacecraft to the gui