Tweaks and bugfixes for 0.39.1

The NyxBarren biome is now significantly more rugged.
Ghostflame orbs now require only 4 phantom resin to craft.
Blank charms now require phantom resin instead of orichalium.
Viscous shadows now have a yield of 2 per recipe.
Viscous shadows now have a slightly above zero hardness.
Summoned skeletons now have a follow range of 12.
Wicked necromancers now throw splash potions of healing II when
fighting undead entities.
Wicked necromancers now fight each other one-on-one when they aren't
fighting players or passive mobs.
Fixed a bug wherein gatestone generation wouldn't work.
Fixed a bug wherein the generation of spiny melons would crash th game.
Limited the scope of BiomeGenNyxBarren's roughening algorithm.

The terrain is now roughened if and only if the biome generator for a
column is an instance of BiomeGenNyxBarren.