Group up style information changes and report at the end of an op batch

Operation batches that modify a large number of paragraphs (or repeatedly modify the same paragraph) can cause numerous unnecessary style change events to be triggered. Rather than reporting these instantly, track them as they occur and emit the style change summary on batch end.

Related to #610.
``valueGot`` makes no english sense, so I'd expected more people would be confused if I changed it to that. Most of these terms are already in relatively wide use in WebODF source (e.g., ``LazyStyleProperties``), so I simply assumed they were quite well known.

Oh well... will ponder terminology a bit then and see if I can find something clearer.