Actually agree with physics

[zenith391]

Stella Dei currently has many mechanics, none of which use any real physics unit, thus those should be converted:

• Planet radius (preferably express it in km, currently most values are expressed relative to it, with 1 being the radius of the planet)
• Temperature (already expressed in Kelvin)
• Physically accurate temperature behaviour
  • Conduction
  • Thermal radiation
  • Solar illumination
  • Any other non-negligible phenomena affecting temperature in a way that a basic simulation (liquid water + poles on north and south) can't work without that
• Water elevation (preferably express it in km)
• Physically accurate water behaviour (that is, as a flat layer like it is currently, as particle simulation would take too much computing resources and be mostly useless)
• Decide of what materials the planet is made of, in which layers and in which quantities

Once all of those are done, progress on other features may continue.

[zenith391]

Planet radius done in f357345 and water elevation completed in 2505fb6

[zenith391]

Currently the temperature simulation assumes the planet is entirely made of SiO2 (silicon dioxyde). It evens ignore the water level (which needs rework to be with mass anyways), but I'm almost done

[zenith391]

Water level has been reworked to use mass instead of 'elevation', but the behaviour is still not physically accurate.
However, I'm reconsidering whether or not it is a good idea to use Navier-Stokes for it as solving the equations take a lot of CPU time.