SA theme tweaks

- Add two new logos to the header
- Hide the "home image" on the front page
- Make the "site intro text" slightly larger and more space between
  lines, to make the text box equal height to the search box next to it
  (the text itself is specified in the /ckan-admin/config page, not
  hardcoded, this font size and line height works with the text as
  currently specified there)
- Add two new logos to the footer