XMLUI: Set max-width for item thumbnails in CSS

Now that we're generating larger PDF thumbnails, we need to restrict
the size in CSS.
XMLUI: Set left indent for files list table
dspace.cfg: Enable larger max thumbnail sizes
dspace.cfg: Enable XPDF filter for PDF thumbnails

Requires XPDF to be installed and configured, see section 6.4.2 of
the DSpace manual for more information.
xmlui: Fix double style tags in ILRI theme
xmlui: Re-work XMLUI themes for new thumbnails

When using filter-media with xpdf we can get automatic thumbnails
at a much higher resolution (300x300px right now), so we need to
hard code a sensible thumbnail size in the XMLUI so the browser
scales it down (otherwise it uses $thumbnail.maxwidth from dspace.cfg
and the XMLUI gets ugly due to the xsl performing CSS math based on
that value).