Added base calls for print document events and added extra events.
Added base calls for print document events and added extra events.

The base calls in the overloaded print document events were missing. They've been added to the bottom of the implementations. Two extra before events have been added if code needs to be injected before Pdfium does its work.

Bug: #50

pvginkel/PdfiumViewer,pvginkel/PdfiumViewer