Automod improvements

[Arcensoth]

TODO

• Add normalization to message_content_contains condition
• Add a new log_message action (with content, emoji, fields, etc) to help streamline logging
• Add member_created_at, member_joined_at, and member_for fields to member join/leave events
• Add an overridable "get extra fields" method that can be used by events to provide additional fields
• Implement configurable permissions (per-role?) for managing automod per-guild
• Use AllowedMentions to enable/disable pings in certain cases