2.x calendar changes

[MarkBaker]

This is:

- [ ] a bugfix
- [X] a new feature
- [ ] refactoring
- [ ] additional unit tests

Checklist:

• [X] Changes are covered by unit tests
  • [X] Changes are covered by existing unit tests
  • [X] New unit tests have been added
• [X] Code style is respected
• [X] Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• [ ] CHANGELOG.md contains a short summary of the change
• [ ] Documentation is updated as necessary

Why this change is needed?

Calendar setting (1900/1904) from a loaded spreadsheet is now saved against the spreadsheet, allowing handling of multiple spreadsheets with different settings, rather than maintained as a global setting. The static global setting is still used for calcuation/formattig, but is set from the spreadsheet when required. This does mean it's dangerous to rely on the old setting, because it is no longer consistent