The previous built-in reference doc had only title and content
layouts. Add in a section-header slide and a two-content slide, so
users can more easily modify it to build their own templates.
Golden files needed to be regenerated. Checked on MS PowerPoint 2013.
This file wasn't used in the production of documents. It's supposed to
be a thumbnail of the current document, and we can't actually produce
that ourselves. It turns out that the file contains a nonfree ICC
color calibration file, so the best thing to do would be to remove it
altogether.
Fixes: #4588
