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!