Async loading
- Now obtains heads asynchronously to prevent lag on startup
- Informs players if not all heads have been loaded yet
Category permissions
- Now requires permissions for each category in the format
he.category.<category_name> - If 5 or less categories are available to the player, the GUI will use a single chest rather than a double chest
- If 3 or less categories are available to the player, the GUI will center the menu items
- If no categories are available to the player, a barrier block will appear informing the player