Minor Change to LimboProvider

Changed the condition on LimboProvider.canRespawnHere() so that players
can respawn in Limbo even if LimboEnabled is false. LimboEnabled only
controls whether players are sent to Limbo when they die in a pocket. It
does not prevent players from ending up in Limbo because of Monoliths.
If Hardcore Limbo is enabled, it stands to reason that people should be
respawning in Limbo anyway.
Fixed Crash with ChickenChunks

Fixed a nasty crash to desktop. It happens when ChickenChunks is
installed and a new world is generated with HardcoreLimboEnabled = true.
It appears that ChickenChunks forces a chunk to generate in Limbo if
LimboProvider.canRespawnHere() = true, which is the case if hardcore
Limbo is enabled. Our Monolith and gateway generation code runs as a
tick handler instead of through standard world gen calls. I believe
Limbo is unloaded immediately after the chunks are generated because no
players are around. That would cause DimensionManager to return null for
Limbo because it's not loaded, which would crash our code. We probably
dealt with this for Monoliths by adding a check. Now it happened again
because we didn't take precautions while calling the gateway generation
method. I've added code to forcefully load Limbo if it's not loaded.
Changed Default Provider and Biome IDs

XombyCraft has been kind enough to research which provider and biome IDs
are used by major mods. He found some ranges of free IDs and suggested
changing our defaults to sidestep conflicts with Biomes o' Plenty.