Cleaned up obsolete code in PocketProvider and fixed the assignment of
hasNoSky so that it actually applies. Also overloaded getActualHeight()
so that we return 256 despite hasNoSky = true - the default MC behavior
is that we would return 128 in that case. Also undid a previous change
to EventHookContainer - players that die in pockets will respawn in
Limbo, again.
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.
