Ability to "watch" user

[emmiegit]

Staff may designate a channel for watch output (see logging cog issue).

Members can be "watched" or "unwatched". When watched, they are added to a list with associated items to "watch" for. E.g., nickname changes, role pings, joining, leaving, receiving/removing roles, mentions, messaging in a channel, messaging anywhere, reacting, username change, etc. All these events are rendered as embeds and sent to the configured channel.

Staff may modify the watched events, or remove them from the list.