Bug 34627: CMS pages do not correctly display the opaccredits footer

Bug 34627: CMS pages do not correctly display the opaccredits footer

This patch corrects the page structure of CMS pages in the OPAC so that
the contents of the footer, including opaccredits, OpacKohaUrl, and the
language selection bar, are displayed correctly.

This patch contains indentation changes, so ignore whitespace when
viewing the diff.

To test you should have these settings:

- OpacKohaUrl enabled in system preferences
- Some content in the opaccredits HTML customization region
- Some content in the OpacNav HTML customization region
- At least one translation installed and enabled
- The opaclanguagesdisplay preference enabled
- The OpacLangSelectorMode set to "only footer" or "both top and footer"

- Apply the patch and go to Tools -> Pages and create a page with the
  display location "OPAC."
- Open the OPAC link for your newly-created page and confirm that the
  page looks correct:
  - The "main" region with the white background should contain the
    breadcrumb navigation, the sidebar OpacNav content, and the contents
    of your CMS page.
  - The opaccredits and OpacKohaUrl content should appear below that
    region.
  - The language selection footer should be at the bottom of the page.

Signed-off-by: Pedro Amorim <pedro.amorim@ptfs-europe.com>
Signed-off-by: Aleisha Amohia <aleishaamohia@hotmail.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 7d5dc65867a55045fa32189d177379e70ecf5725)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>