Refactor !dm command

[potatoboiler]

important:

• make it easier for a user to send multiple dms to multiple people at once: (thoughts, -m and then a list?)
• two messages, one to query users, and the others to set the message. message/error order:
• make non pb unable to use !dm altogether (move the non pb way earlier)
• remove genreic exception printout (lol)
• get me to procrastinate less pls
• add logging to prevent anonymous pb abuse?