Fix NPE on player interactions with air (apparently this causes event#getClickedBlock to be null)
Added a new shopBlocks stringlist to the config section
Any block that is a Nameable Container can be a shop. The defaults add Chest, Trapped Chest, and all shulker box colors to shopBlocks.
You can add other blocks such as Furnaces, Droppers, etc. if you so desire. Or remove some of the ones specified above. Just be aware that this only works with blocks that can be named and are a container.
