Pass #1 for Better Dungeons 2 support

Removes poor quality loot
Adds specification for new loot, to be approved before implementing
First serious dungeon spawning pass

After confirming the dungeons spawned at all, this pass gets them to spawn often enough to make people want to explore yet rare enough not to overburden the worldgen process and to make finding the dungeons novel.

Quality loot drops are up next.
Repeat pass

Made the mundane-feeling Underground Dungeons (and Slime Caves) rarer, raised the frequency of more novel dungeon schematics.

Also changed the dungeon walls to look less crappy
Rewrote specification.txt

This should be a lot more practical as it was derived from looking at the in-game NEI feed.
Loot list compiled

Tested and working in dev builds

Actually works a lot better in practice than I expected.
RR 2.6.9.0-EXP update

The only change from the last EXP release is the addition of BD2.
Merge tag 'tags/v2.6.9.0' into serverExp