Fix error with update checker permission

Added new command (/clean <world>), the <world> argument is not required
Added new permission (itemcleaner.clean), to use (/clean <world>) command
Added new variable %world%
Added new variable %removeditems%
Removed command (/itemcleaner cleaner <enable/disable>)
Removed permission (itemcleaner.cleaner)

Added two lines of (messages.help), exactly this lines (- '&e/clean &7Clean items in the groung'), (- '&e/clean <world> &7Clean items in the groung in selected world')
Added a line of (messages.permissions), exactly this line (- '&eitemcleaner.clean &7Allow to use &e/clean &7and &e/clean <world>'
Removed a line of (messages.help), exactly this line (- '&e/itemcleaner cleaner <enable/disable> &7Enable/Disable auto clean funcion')
Removed a line of (messages.permissions), exactly this line (- '&eitemcleaner.cleaner &7Allow to use &e/itemcleaner cleaner <enable/disable>')
Removed message (itemcleaner-cleaner)
Removed message (cleaner-enable)
Removed message (cleaner-disable)
Added new message (config.clean-clean-message)
Added new message (config.clean-world-not-exist)
Modified (config.clean-message) new name (config.auto-clean-message)
Added in message (config.auto-clean-message) new possible variable %removeditems%

The removed command is because when use the command, all coments disappear.

If you update the plugin, is highly recommended to delete the config.yml file from the /plugins/ItemCleaner folder and then restart the server.
If not, manually remove and add at least the grey section or it will not work properly.

Removed possible NullPointerException when PlayerJoin and Check for updates

Added update checker