Add operator_id field to users

[RyanTG]

Add a field to users table called operator_id so that users can be associated with a particular operator record.

Highlight a user who is an operator (different color user name? icon? highlight the entire comment?).

I think this would entail adding "has_many" users to operators.

A stretch goal could be to base the operator emails off of this. Like, rather than having a single email for each operator record, instead the email digests get sent to users that have that operator_id.