Update to Head

Update to head

Added onCreatePage to PDFCreationListener.
Added fireOnCreatePage to PdfBoxRenderer - by default this just creates
a PDPage and adds it to the PDDocument (old behavior).

This allows the user more control over the page that is created and also
control when (or if) a page is to be added to the PDDocument.

danfickle#8 Online sandbox now at RC18. [ci skip]

(See danfickle#334)

Based on the suggested by @danfickle, reverted the changes to
PDFCreationListener and PdfBoxRenderer, instead a PageSupplier can be
set via the PdfRendererBuilder.

The PageSupplier.requestPage allows the user to create a new page or
supply an existing one where the Html will be printed.

PdfRendererBuilder implements PageSupplier and simply creates a new page
and adds it to the PDDocument.

…into open-dev-v1

Added a brief explanation what "shadow-pages" are to the PageSupplier.
As @danfickle pointed out, the current-page index (i) should be used as
pageNumber argument for PageSupplier in PdfBoxRenderer when building the
shadow-pages and not the pdfPageIndex (which at this point has already
been upped by one).
Also first call to PageSupplier should (for the first page) should be
with pageNumber 0, not 1.