Sync with webodf fc3a4e615597be18da1e23e03302ef472b9a95e5

Apart from improving some performance with text selections, this PR fixes the OT logic for InsertText and SplitParagraph.

From now on, multiple people inserting text or splitting a paragraph at the same cursor position should give the same result at every client in collaborative mode, with no more errors or sync inconsistencies there.

Fixes #89.