PDF Icon for candidates

[chriswales95]

In PR #56 the PDF icon for candidate files was removed due to reasons explained in the PR.

We need to decide if we want the PDF icon to remain and if there's any reason not to.

@dedavidson and I think we should due to UX reasons. It's helpful to know you're opening a PDF instead of another page. I believe standard Drupal does this type of thing anyway and presents a file icon with the file size.

We may need to create some sort of plugin for this.