Sprinkle around some shrikes (and other quick vault population tweaks)

Mostly additions to Cocytus and Zot, though both caustics and shards
have lone visitations in a miniscule slice of some Depths vaults.
Also, caustics replace some lair end vault representatives for Lair
zigs, shard shrikes slip into Ice zigs, and orc zigs don't place excess
orcs anymore (since it doesn't really add to the threat and gets in the
way of placing marginally more dangerous stuff in later zigs).