Slash Commands and Message Components

• Updated to discord.js v13. With that, the bot now functions using slash commands. The custom prefixes are all gone, as well as the ! default prefix. The global prefix is now / across all servers.
• The setprefix command has been removed.
• The option to view info about a specific command has been removed (Discord does that for you via the slash commands menu).
• The help command links are now shown in message buttons.