Add CSS for non <fig> wrapped images

As we need images for the DFID Finder, uploading attachments and
prepending a bang to the attachment code parses it as an image,
althought it's outside of a <fig> tag. This CSS means that it stays
within it's container and can resize.
Merge pull request #36 from alphagov/add-css-for-govspeak-images

Add CSS for non <fig> wrapped images