Refactor PacketPipeline to use SimpleNetworkWrapper

Should fix leaking packets: http://www.minecraftforum.net/forums/mapping-and-modding/minecraft-mods/2185602-beta-1-0-better-overworld-aka-project-zulu-now?comment=80

Didn't get a change to test on a dedicated server as apparently eclipse requires some UUID argument in the new versions of Forge to connect in eclipse. But the internal server works.