Flamethrower fixes.

Fuel now burns, even without an auto-ignition temperature, which was a silly way of doing things.
Mobs no longer ashify since their proc is changed.
Flamethrowers now spread more fuel and burn more consistently for it.
Atoms now have volatility, so they can burn more if they have less fuel.
Fuel now ignites correctly when throwrn, and fuel itself no longer has the issue of catching fire intermittently, as it now burns without needing an ignition temp.