Bukkit

The world management have been added:

- world command to manage world rules

- zones are added, the zones are stored in cloud in snapshots and can be reverted any time

- groups to control the rights

- gates allow to teleport from one world to another

- tokens to be used to assign the rights dynamically

- user command is added to set the user's alter-ego (alternative identies)

- blocks are added to control the chests and doors

- spawners are added to manage the entity spawning behaviour