New port: print/pdfstitch

Pdfstitcher can transform a regular multi-page PDF into a single-page PDF,
which displays the pages in a grid.

While there are other tools that do the same, pdfstitcher focuses on the
following features:

• Crop pages to a certain size
• Adjust the crop position per page

WWW: https://github.com/sur5r/pdfstitch

PR: 221396
Submitted by: Stefan Hagen <ports@textmail.me>
Reviewed by: ultima