#4 Late signup list calculation needs improvement

[Tim Mensch]

The late signup list is currently limited to members who have sufficient tokens to eat meals. This is incorrect: It should be limited to members who had a sufficient number of tokens to eat a meal at the time of the meal sign-up deadline.

A query of the token transfer table by the date and time of the deadline should produce this value for each person, and if this value is >=-5 tokens it should list them (since it's going to be difficult to calculate whether or not a person was signed up to work at the time of the meal, and I don't want to clutter the database with lists of people-qualified-to-eat-at-each-meal).