Add "UNIQUE" option to Group filtering

Add a UNIQUE clause to the Group Filtering options.

Some of the ways our tables are set up, the group filter returns rows with identical Emails. That's fine because it's the truth, but when we send out email communication, we don't want it to send to one person 10 times.

Adding the ability to put UNIQUE, or even just an auto de-dupe when sending the emails out would be amazing.