try generating excel as one class per workbook, not one class per sheet

[turbomam]

There are roughly 11 checklists and 24 extensions. Those combine to form 264 additional templates.

Stretch goal: organize the output so there's no one folder with ~ 300 Excel files

either checklist based or extension based

or maybe we should just use a Makefile rule that moves after generation

[turbomam]

Or a worksheets to workbooks Excel splitter?

see https://bard.google.com/chat/c0f71624d1baaa91

[sujaypatil96]

Accomplished in PR #733