Create a level on a planet surface

[smerkli]

Idea: Use the available mechanisms (space race, space boundaries) to build a planet-surface level

Since we have space boundaries now, an idea would be to make two concentric spherical space boundaries and have the player spawn between them. Then one could add a model inside the smaller sphere, giving the player the possibility to move around on the planet's surface. Using other shapes, one could then for example build a spacerace on a planet's surface.