Show inline attachments on worldwide org pages.

Use the govspeak_edition_to_html helper, which requires the whole Edition object
rather than just the body. To enable this, make HasCorporateInfo.about_us a
public method.
Prevent errors being caused by nil parameter

Not all worldwide organisations will have an about page, or at least
they won't until one is created.
Merge pull request #1640 from alphagov/worldwide_cips

Show inline attachments on worldwide org pages.
Use Ghostscript to generate PDF thumbnails

ImageMagick cannot convert PDF to images by itself and instead delegates
to Ghostscript. By bypassing ImageMagick and going to Ghostscript
directly, we see a big improvement in thumbnail generation speed:

	Test file 1 with ImageMagick: 30.7 seconds
	            with Ghostscript:  1.5 seconds
	Test file 2 with ImageMagick: 30.7 seconds
	            with Ghostscript:  1.2 seconds
	Test file 3 with ImageMagick: 31.4 seconds
	            with Ghostscript:  1.7 seconds
Merge pull request #1645 from alphagov/faster-pdf-thumbnailing

Use Ghostscript to generate PDF thumbnails