Adds support for multiple comments on the same text object.

[rodrigoq]

Description

Fixes #2109

Changed AbstractElement->commentRangeStart and End for a collection (commentsRangeStart and End) that accepts multiple comments for same element.

For consistency in names maybe a rename is due for Word2007 Writer AbstractElement writeCommentRangeStart (and End) to writeCommentsRangeStart, since it now iterates over the collection, a plural could go, I didn't change it because there were many files and made the pull request more complicated to follow.

Checklist:

• [ X ] I have run composer run-script check --timeout=0 and no errors were reported
• [ X ] The new code is covered by unit tests (check build/coverage for coverage report)
• I have updated the documentation to describe the changes