Partially overhauled our command classes. Added DDCommandBase - it
extends CommandBase and acts as a new base class for our commands. It
removes a little redundancy in our code and provides increased
convenience. Removed the static fields for our commands in
mod_pocketDim. There was no point in keeping them when nothing was using
them. Changed in-game command names to be shorter yet relevant.
Converted all commands to singletons so proper instances can be
retrieved if necessary. Migrated some of the custom dungeon start/ending
logic to DungeonHelper and made customDungeonStatus private. Except for
data objects, we shouldn't be exposing state variables like that without
any kind of checks. I've rewritten the code in some commands but it's
been quite tiring. Still need to fix up lots of things.
