Merge pull request #56 from Matchlighter/master

Reverted back to my function for finding the nearest gate.
Squeezed a bit more performance (avoid SQRTs) in StargateNetwork#findNearestStargate().
This is what I wanted to do in the first place!
Adds a bit more into the Stargate API, so that mods can reserve specific addresses for their dynamic world loaders :)
Added prefixExists() to (I)StargateNetwork.