Update to Discord.js v13 (Discord API v9)

[suvanl]

This PR contains fixes for breaking changes caused by the update from Discord.js v12.5.3 to v13.0.1:

• As a result of updating to D.js v13, the minimum required Node version increases to 16.6.x. This has been reflected in the README and in the Node version check that runs at every startup.
• Update channel type names - they are now uppercase and in line with Discord's naming conventions (e.g. text -> GUILD_TEXT).
• Client constructor: move intents from ClientOptions#ws#intents to ClientOptions#intents and enable CHANNEL partial to ensure DMs are received.
• Replace all instances of member.hasPermission() with member.permissions.has().
• Rename "message" event to "messageCreate".
• Replace collection.array() with [...collection.values()].
• Replace fetchBans() with bans.fetch()
• Replace guild.member(user) with guild.members.cache.get(user.id).
• Send embeds and files using MessageOptions (e.g. channel.send(embed) -> channel.send({ embeds: [embed] }))
• Stop using guild.owner() as it has been removed.
• Update "server" command to show the boost tier number (0, 1, 2, 3), not the name (NONE, TIER_1, etc).
• Capitalise first letter of all strings inside the message.reply() method as inline replies are used now.
• Use TextChannel.sendTyping() instead of startTyping() and stopTyping().
• Fix the awaitReply core function by updating the object in the awaitMessages function to match the new required format.

Other changes include:

• levelCache Map: swap key-value order (to make more sense in contexts where the permLevel int needs to be retrieved).
• add "guild" and "guildinfo" aliases to Server command.
• use optional chaining where appropriate (User command).