* Track Changes: emptying a paragraph no longer turns its mark into the text's revision (#864)
Paragraph::delete copies the formatting of what it deletes onto the paragraph
mark when it empties the paragraph. That copy included the revision ids, so
accepting a tracked deletion of a whole paragraph text made the mark a deleted
mark too, and Accept All joined the following paragraph. Rejecting typed text
in an empty paragraph likewise rejected the paragraph mark. The mark now keeps
its own ins, del and fmt_change.
* Credit Silvertree2010 in the About window
* Docs: update the progress docs for this change
* Docs: Last reviewed stays as it was
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Co-authored-by: Brandon Thomas <echelon@gmail.com>
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