Header/Footer Images Expand "Location"

[oleibman]

Fix #484. Fix #1318. Both went stale a long time ago. The images can currently specify their location as Left, Center, or Right. However, they also need to specify their type - first page, even pages, or odd pages (which is what is used when neither of the others is applicable). This is accomplished by adding 18 new constants to Worksheet\HeaderFooter, any of which can be specified as the second argument to HeaderFooter::addImage. Somewhat surprisingly, no changes are required to Xlsx Writer or Reader.

Xls Reader and Writer support header/footer, but do not support using images in them. No other readers nor writers support header/footer.

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