Print PDF Letter for Contacts task - page orientation is 'landscape' but should be 'portrait' for letters

This task uses the same function as the CiviReport PDFs - and the page layout is currently hardcoded to 'landscape' (since that's appropriate for report pages). However, expected orientation for letters is 'portrait'.

Add a parameter to CRM_Utils_PDF_Utils::html2pdf to allow override of page layout (default can still be 'landscape'). Then modify CRM_Contact_Form_Task_PDFLetterCommon to specify 'portrait' layout (line 198).