Replaced Hashtable with HashMap

Replaced all instances of Hashtable in our code with HashMap. I had
never given that much thought until Steven mentioned it. HashMap is a
better alternative for our code.
Renamed all singleton create() to initialize()

Renamed the create() function of DDProperties and DungeonHelper to
initialize(). Why? Because it was bugging me. <.< That is all.
Overhauled RiftGenerator

Overhauled RIftGenerator. The code is significantly more readable now.
It's commented and much more compact. I also removed all fields from
RiftGenerator - they were unnecessary and using them increased the risk
of buggy code. Made the code rely solely on the Random instance provided
by MC, meaning our rifts and gateways will be tied to the world seed.
Tweaked the code slightly so that clusters of rifts and gateways can
never generate in the same chunk. This was previously possible, although
highly unlikely. It's a work of art now. <3
Trivial Changes

Made trivial changes to DungeonHelper. Just some spacing and a note to
check something in the future. Need to commit to change branches.