Add spacing between file navigation buttons and review UIs.
Review Request #9358 - Created Nov. 10, 2017 and submitted
The new file navigation buttons were pressed pretty closely against the
review UIs, making them feel a bit cluttered and noisy. This change
simply adds some spacing between the buttons and the review UI, helping
to improve that look and feel.
Tested with and without previous and next attachments to check for spacing.
Tested that other elements (like the draft banner) were not impacted.