Changed damage to player to x0.5 and fixed the preview image

Fixed preview and thumbnail. Changed damage to zombies from x4 to x6 for better balance IMO (zombies still took too long to die even for the undead). Damage to players from x0.25 to x0.4 because fire was too nerfed with x0.25 in my tests. It made it feel not very dangerous to run through.

Added compatability for b42.