Xlsx Writer Honor Alignment in Default Font

[oleibman]

Fix #3456. A mysterious implementation by Excel. The style tags have an attribute applyAlignment, which nominally says whether or not the style should use its own Alignment. Except ... Excel ignores that attribute and uses the alignment tag if it is supplied ... and, another mystery, uses not the default style for the spreadsheet if not supplied, but rather uses the default alignment style for all spreadsheets even if the spreadsheet's default style uses a non-default alignment. I am changing Xlsx Writer to generate alignment tag unless the alignment matches both the default alignment for the spreadsheet and the default alignment for all spreadsheets (which I expect to happen most of the time).

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• 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 and a link to the pull request if applicable
• Documentation is updated as necessary

Why this change is needed?

Provide an explanation of why this change is needed, with links to any Issues (if appropriate).
If this is a bugfix or a new feature, and there are no existing Issues, then please also create an issue that will make it easier to track progress with this PR.