make draconium less abundant in overworld

[felixfour]

the GT6 deepslate layers currently spawn a lot of draconium in a large area (it's not as dense locally but has more average density than a single ore deposit)

with DE installed you already get plenty from the end in comets; i set it here to be 2.25 times less frequent and only appear in magical biomes (since it's much more powerful than the magical ores that already appear in those biomes' deepslate layers)

[GregoriusT]

Please be aware, the reason it generates like that is because it generates like that in the Overworld without GT too, the funny thing about it is, Draconium Ore is usualy invisible in the Overworld, so you only tend to find it once you harvest it with a Quarry or something along those lines.