Added new config option "banned-item-IDs" for admins to ban items.

To ban a specific item, set "enable-banned-item-IDs" to true then enter the item ID between the brackets of banned-item-IDs located in bukkit.yml.

Example:

banned-item-IDs: [2000, 5000, 10000]
enable-banned-item-IDs: true

This would ban items with ID's 2000, 5000, and 10000 which essentially
prevents them from being used or activated.