Auto-update attendance frequency

[dehnert]

Gate is split up by attendance frequency -- "every", "monthly", "rarely", "never" -- which limits scrolling in the common case of frequent attendees showing up. We should automatically update this.

I think my theory was to do something like "count how many times somebody has showed up in the last month and the last year", and then:

• If they've come in the last month, put them in every or monthly
• If it's at least like 20 times in the last year, every
• If it's at least four times, monthly
• If it's ever, rarely

(Maybe we look at the entire SquaresDB attendance history for rarely vs never, not just the year.)

I think this should be a batch process. I'm not sure whether it should be weekly or like monthly. I guess weekly seems fine?