Bug 28662: Not possible to log out of patron account in OPAC with JavaScript disabled

Bug 28662: Not possible to log out of patron account in OPAC with JavaScript disabled

This patch adds a "Log out" link to the OPAC header which is hidden by
CSS when JavaScript is enabled.

To test, apply the patch and rebuild the OPAC CSS
(https://wiki.koha-community.org/wiki/Working_with_SCSS_in_the_OPAC_and_staff_client).

 - Log in to the OPAC with JavaScript disabled in your browser.
 - In the header next to the logged-in user's name there should be a
   "Log out." link.
 - Confirm that it logs the user out.
 - Enable JavaScript and repeat the process to confirm that the new
   logout link doesn't appear.

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>