Make OdtDocument.convertDomToCursorRange
accept two constraining functions, indicating
the rounding direction at each endpoint.

In SessionController.selectRange's call to
OdtDocument.convertDomToCursorRange, fix it
to restrict the endpoints of the cursor range
within their original paragraph containers.

This fixes issues where indenting/paragraph-styling
completely-selected paragraphs (that had their
beginnings already direct-styled) would also
indent/style their previous paragraphs.

Thus, triple-click selection no longer bleeds
into the surrounding paragraphs.