Further Metallurgy corrections

Based on feedback (i.e. Lambert saying the Iron oregen was "perfect"), Iron-style ore distribution has been applied to other common ores, adjusted for intended rarity. This should result in a net reduction of available ore without badly damaging its availability whilst spelunking.

Additionally, after examining the heightmap, the 2.3.5 range chances to copper and tin risked reducing our three core mining bands to two, and have been contracted again slightly, sitting halfway between the 2.3.4 value and the 2.3.5 value.

Finally, Platinum was still too common! Especially Nether Platinum after the buff.