More cleaning up errors and code. There were a lot of things that needed
simplifying. Rather than fix the 3 or 5 copies of the same function
throughout the code, I made an effort to use the same function and
delete its copies.
Created the BaseItemDoor class to hold all the basic door item methods
that don't vary between types. That helped cut down on fixing things.
Also renamed the door item classes to match their in-game names.
There is still a ton of duplicate code out there.
Replaced several core classes from DD with new classes to enforce
integrity checks. Rewriting everything that depended on those classes is
a massive undertaking but it should simplify our code and prevent the
many bugs we've seen lately. The rewrite isn't done yet, just committing
my progress so far.
