Optionally determine physical correct amount of oblation

[fibonatic]

I think it would be useful is there would be an extra option when using PQSMod_PFOblate, which would set the radius of the poles and the equator to the correct ratio's depending on the planet's mass and rotation period, which would agree with some laws of physics.

Namely when using potential energy the relation between equatorial and polar radius can be found to be equal to: Rp = 2 * G * M * Re / (2 * G * M + omega^2 * Re^3) where Rp is the radius of the poles, Re the radius of the equator, G the gravitational constant, M the mass of the planet and omega the angular velocity in radians, so 2 * pi divided by the sidereal rotation period.