Fix some small bits in base.html.

Fix some small bits in base.html.

1. Add a trailing slash to the mediagoblin.org URL.
   (The string changed anyway, so translations are not
   affected more than already.)
2. Order was wrong for those two at the end (old version):
     {% endblock mediagoblin_body %}
     </div>
3. Fix some little indenting issues.
4. Remove some useless space from the output.