Lots of fixes and new features

• Fixed bugs on server reload (MessageTask.php)
• Update database data on plugin reload
• Implemented cancellable events
• Allow player unregistration from console
• Block player joining with the same username when the player is authenticated
• Block EntityDamageEvent for not authenticated/registered users
• Fixed logout
• Fixed permissions for /serverauth command (Thanks to @Pub4Game)
• Fixed a /give command related bug (Thanks to @Pub4Game)
• Kick players after n° of failed login attempts feature