Analyse attendance relative to rosters

[tbar0970]

Some people only show up when they are on the roster to do something.

It would be valuable to be able to spot this phenomenon in Jethro. Some ways:

1. In an individual person attendance tab, show an "R" for dates where the person was on a roster. Then you can look at whether all the green boxes have Rs in them.
2. Enhance the attendance filter in person reports, something like "whose attendance at [their congregation] was [less than] 25% in the last [9] weeks, [x] excluding weeks where they are rostered"
3. Might be other approaches?