Fixed several bugs on blood feeding (entity died or damaged during feed etc.). Blood flask restores 30 health points (big flask restores 60). Gravedigger's and brigand feeding adds 30 points, ghoul feeding (spell not implemented yet) takes 20 points. Added blood poisoning (drain is 1 point per second). Maked antitoxin work. For testing only - gravediggers now have poison blood (will be reverted back next commits).