Added functions for generating destinations for some link types that we
hadn't included yet - player-made exits, trapdoors, and dungeon exits.
The player-made and dungeon exits still don't generate anything, but
there's a single function where we can write up the code:
DDTeleporter.generateSafeExit(). Also added some simple code for listing
root dimensions in PocketManager. None of this has been tested yet!
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