+ Added a check for AIR material to prevent glitching plugin.
+ Added a /stacks reload command which requires permission ("STACKS.RELOAD").
+ Added a lang.yml file with some messages for reloading, permissions, etc.
+ Added cached materials so can restore old stack amounts on reload.
+ Fixed an issue with blacklisting items.
+ Changed blacklist to "whitelist" as this was incorrectly worded.
+ Improved some areas of the code.