Bug 22680: OPAC language footer not positioned correctly

Bug 22680: OPAC language footer not positioned correctly

This patch modifies the OPAC CSS so that the language-selection footer
is positioned correctly.

To test, apply the patch and rebuild the OPAC CSS.

- Enable one or more translations in the OPAC
- View a page in the OPAC which can display in your browser without a
  vertical scrollbar (for instance, the OPAC main page with no news
  items or OpacMainUserBlock).
  - The language-selection footer should appear at the bottom of the
    screen. At smaller browser heights the footer should scroll
    offscreen.
  - Test with content in the opaccredits system preference, and with
    OpacKohaUrl enabled. The footer should still be positioned
    correctly.

Signed-off-by: Liz Rea <wizzyrea@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit d8a196cc9decd19a5401907adc64c7dee80a0c55)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>