Ability to send notices from staff

[charmander]

• can streamline processes like re-rating unless we decide there are situations where it would be bad to send a notice about re-rating (I don’t think there are? separate batches of re-rating can be merged automatically, have an explanation provided retroactively)
• can have their own group at the top of notes
• not attributed to a particular staff member, as responses should be visible to everyone and not dependent on the sender’s continued staffiness