Tweak the math for the compound diffusion effect speed

[hhyyrylainen]

I think the surface patches will need more aggressive diffusion between each other to not have as big concentration differences between gases that should basically be pretty uniform due to the atmosphere being mostly uniform on planets. I'm proactively opening this issue as someone will probably complain about this once 0.7.1 is out. The hardest part is basically just coming up with the new math formula for how much compounds should move between given patches.