Quick Fix for Limbo Music Crash

The following small change deals with a strange background-music-related
crash. Wasn't this issue fixed for Jaitsu and Aether II? I'm not sure
what's the cause but I've added a check to prevent the NPE. Please deal
with this most robustly in the future.
Merge remote-tracking branch 'upstream/master'
Minor Changes

Cleaned up the code for placing Vanilla doors on rifts in
EventHookContainer. Unfortunately, there's a section that I don't
understand and that I feel has a bug. Remember that comments are very
helpful.
Added More Dungeons

Added Cere-JumpPass, Cere-TransferTunnel, Cere-GreatHall,
SK-WatchedForkLeft, and SK-WatchedForkRight. Made a minor change to
SK-RaceTheLight.
Added Settings and Minor Preemptive Fix

Added a setting to DDProperties for controlling the max distance that
players can be moved randomly when they're sent to Limbo. We previously
had a setting for the same except for leaving Limbo. Cleaned up some of
the related code a little. Added another setting for the chance of rifts
dropping World Thread on block destruction. Also fixed a potential NPE
in EventHookContainer that could arise theoretically arise if a
non-Vanilla door was attached to a rift.
Minor Change

Minor name change
Added Subtree Searches for Dungeon Packs

Added a new setting to dungeon pack configs called
"DuplicateSearchLevels", which allows us to configure how many levels up
of the dungeon tree should be checked to avoid duplicating rooms used in
that subtree. In other words, it lets us avoid repeating rooms used in
neighboring branches of the dungeon. The setting has been added but it's
not fully supported yet - some additional code is needed in
DungeonHelper and it's not trivial to implement. I took a break because
doing it wrong could break dungeon selection.
Fixed Tooltip for ItemStabilizedRiftSignature

Fixed the tooltip for the Stabilized Rift Signature - it was a copy of
the Rift Signature's tooltip.
Improvements to Dungeon Selection

Changed the code for dungeon selection in various classes so that rather
than allocating and passing around the dimension where the dungeon will
be generated, we instead pass around the parent dimension. This
simplifies our code and moves us toward avoiding stray dims when dungeon
selection fails and to solving the dungeon pre-generation problem with
gateways.
Rearranged dd-rift Workflow

Changed dd-rift and dd-random so that rifts are only placed after a
dungeon is generated successfully. We also delete the link if generation
fails to clean up after ourselves. Also changed
PocketBuilder.generateSelectedDungeonPocket() so that its checks are
stricter and we validate dungeons before allocating a dimension.

This resolves one of our old issues: "Rearrange workflow in dd-rift to
prevent rifts from being created if no dungeon gets loaded and to
prevent dimension registration if the dimension cannot be populated"
Overhauled Gateway Code

* Split off schematic-related functionality into BaseSchematicGateway.
* Moved the default implementations of many methods to the base classes
because having a bunch of duplicate stubs all over the place was a
waste.
* Removed methods that were redundant or weren't being used for
anything.
* Added support for importing schematics while ignoring air blocks
through IBlockSetter - now our gateways are copied in without air by
default.
* Fixed bugs that would have prevented the sandstone gateway from
generating.
* Removed the code in generate() that would cause dungeon
pre-generation. We should solve this by attaching data to links instead
and it's not a feature that we're even using right now (everything uses
the default pack).
* Fully documented our functions - it's so beautiful...
Minor Change

Removed a misleading comment from the rules.txt for Balgor
Integrated Balgor Pack and Fixed Bugs

* Set up the necessary code in DungeonHelper so that Balgor is
registered along with the other bundled packs.
* Improved the code for registering bundled packs to reduce the number
of paths we need to hardcode and to crash DD if a pack fails to load. A
crash would be inevitable no matter what since bundled packs are
integral to DD.
* Corrected an invalid generation rule for Balgor. It's set to select
random dungeons infinitely for now. I'll add an exit room later and
change the rule to force an exit. Balgor is still unusable until its
schematics get proper doors.
* Fixed PocketBuilder to actually check the results of validating
schematics before we try to build them. This was causing cryptic error
messages when flawed schematics were loaded (e.g. rooms without proper
doors) and could have caused serious problems during dungeon
regeneration. Don't ignore validation!
Fixed Limbo Gateways and Minor Change

* Fixed Limbo gateways. I accidentally broke them while overhauling
gateways in general.
* Changed references to BaseItemDoor.placeDoorBlock() to use
ItemDoor.placeDoorBlock() instead. We should refer to the original class
that implements the function.
Fixed Limbo Gateways (again)

Forgot to add the line for creating the dungeon link. Done and tested.
Removed Balgor Pack

After finally getting the dungeons to load, I've determined that only
half of the rooms should be included. The three remaining rooms should
definitely stay. That's not much for a pack so I'm going to make some
modifications to the schematics and include them as part of Ruins.
Added Dungeons to Ruins

* Added three of Balgor0's dungeons to the Ruins pack
* Made aesthetic and functional improvements to the dungeons
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.