Extend HTML output for pagebreaks for PDF generation

Make HTML output of pagebreak compatible for the different PDF writers by combining:
http://mpdf1.com/manual/index.php?tid=110 (tested and working)
and
https://code.google.com/p/dompdf/wiki/FAQ (tested and working)
and
http://chandeshparekh.com/css-to-create-new-page-in-php-tcpdf-pdf/

This is a pull-request for this issue: https://github.com/PHPOffice/PHPWord/issues/426