Add support for pricing sextant modifiers on voidstones

[domialex]

Voidstones have this text, along with the sextant modifiers if present:

Item Class: Atlas Upgrade Items
Rarity: Quest
Ceremonial Voidstone
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Item Level: 84
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Players and Monsters take 12% increased Cold Damage (enchant)
Your Maps contain 6 additional packs of Monsters that deal Cold Damage (enchant)
3 uses remaining (enchant)
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Maps Dropped in Areas have 25% chance to be 1 tier higher
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The Maven knew nothing of mercy
until she herself needed it.
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Socket this into your Atlas to increase the Tier of all Maps.