New document link

It's been pointed out that "Create new document" is a little wordier than it needs to be.

@rjc123 made a couple of commits that changed it, which I've edited to the latest version of the text, and then squashed to a single commit. Then I removed redundant CSS that targeted the span that got deleted.

https://www.pivotaltracker.com/s/projects/367813/stories/56498170

Closes #816.