Custom Item API

Features:

• Added CustomBlockActions and CustomItemActions, which can be used to add your own features to items and blocks.
• Items and blocks are no longer saved in an external file, the plugin that adds the block/item should always be in the plugin folder. (The plugin doesn't need to save it themselves, but they need to initialize the block/item every time the server starts)

If you have any questions about these changes you can ask them in the discord.