Started Rewriting LinkData

Created NewLinkData and replaced references to the original LinkData.
Moved it to the mod_pocketDim.core package. Added Point4D, an immutable
point type for 3D integer coordinates with an added dimension ID.
Minor Fixes to Old Dungeons

Fixed the two blocks sticking out in the multilevel maze that made a
staircase unusable. Put a floor in simpleDropHall so it's actually
usable rather than killing the player.
Merging Changes to Master

Merging recent changes to master.
Flipped a Table

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.
Merge pull request #77 from SenseiKiwi/rewrite

Flipped a Table