Add an 8px margin-top to the statement textarea on the profile edit page

8px was chosen to match the margin between the textarea and the H2 heading
on the horn page. In that case, the margin comes from the H2, but here we
have a sentence above the textarea (with the dropdown).
Merge pull request #1025 from rpicard/statement-margin

Add an 8px margin-top to the statement textarea on the profile edit page