mail-server: local DNS (for ORS), password UI, mail autoconfig, various quality-of-life features

Added features:

• Add initial local DNS request feature
• Add no-relay parameter
• Serve mail autoconfig over HTTP
• Add password change page in SnappyMail

• Add password reset feature
• Add utility iptables script for mail-server-relay
• Auto-detect or create standard mailbox folders

Ergonomy:

• Specify "outbound" relay info for clarity
• Move relay-sr-url default to json schema
• Add more info in password.php error
• Publish password initialization URL in slave infos
• Rename (external) relay to proxy for clarity
• Add forgot password and register link

• Add redirect link to password reset success message

Fixes:

• Rewrite conflict handling
• Update JSON schema version
• A relay is requested for reception even when a domain cannot send