Pre-written signs, working visibility, fixes

* Pre-written signs can be created with "/craftz sign". Place it down,
click "Done", and the pre-written text will appear.
* The visibility bar is now actually used, that means the player only
attracts zombies that are in the correct range expressed by it.
* Kick bypass permission was added, so even if kick-on-death is true you
won't get kicked
* When legs are broken, you cannot sprint
* Fix: When reloading, players are now added to the list
* Fix: Players are now being saved in the correct format