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. [Ticket](https://trello.com/c/pSWg7ySv/228-add-styling-for-images-1).