AutoMod, welcome screen and onboarding

Part of the server settings - always loaded, no separate option.

• AutoMod: replacing deletes the server's rules and creates the backup's (Discord allows only a few per type). Repairing only recreates missing rules. Exempt roles/channels and alert channels point to the new IDs. If an alert channel is missing, the rule is created without the alert (or not at all, if that was its only action).
• Welcome screen and onboarding only exist on Community servers. On the same server, onboarding questions keep their IDs, so members' answers stay valid; on another server they get new ones. Answers whose roles and channels are all missing are left out. If Discord refuses to enable the onboarding (e.g. too few default channels), it's set up disabled and the result says so.