[Request] Allow specifying orbital time directly instead of calculating it

[xkforce]

This would make mirroring real moons much much easier because currently the equation used to calculate the time for a moon to complete an orbit is incorrect. (if you look at the code, orbital time is relative to the third power of the average orbital distance which isn't correct. T^2 = R^3 which gives a ^ 1.5 relationship not ^ 3. It also makes it way way harder to work out how to get a specific orbital time. i.e suppose you want to remake Io in AR. Good luck getting the orbit time correct by guessing the parameters needed.