Refactor zipline generation around new ZiplineLaunchPoint component
Allows simple placement of zipline starting points that will automatically find the closest appropriate ZiplineTarget and create a zipline in PostMapEntitySpawn
Ziplines no longer save and are recreated on server restart
Powerline platforms are no longer entities, each prefab now has 2 launch points and 2 target points that will automatically connect or self destruct if it's not possible