Provide a real implementation of export-pagebreak macro

Following EXPORTTOOL-3 we have now a shallow implementation of the export-pagebreak macro.

This issue is to provide a real implementation of this macro. The expected result of this macro is to create a page break at the place where we have the macro when we do a PDF export.

Ideally we would like to have the same effect on the office export but it might be more complicated to implement.