Make hydrogen sulfide diffuse between patches and balance the vent eruption event

[hhyyrylainen]

There wasn't enough time to add that for 0.8.0 so this should be done ASAP after that to make the vent events and hydrogen sulfide levels be better.

[CI09]

So I just make hydrogen sulfide diffusable in json file, no less no more?

[hhyyrylainen]

That's the first step. However I didn't do that for 0.8.0 as I expect it to mess with the game balance a lot. So you need to first do that but then also tweak the vent eruption events and species eating of hydrogen sulfide (and maybe some other effects if I ended up adding a hydrogen sulfide floor, which I can't remember if I made an effect like that) so that the game balance is fine.