Bug 28101: Update breadcrumb markup in the OPAC for consistency and accessibility

Bug 28101: Update breadcrumb markup in the OPAC for consistency and accessibility

Modified breadcrumbs to be accessible, in particular for a
screen-reader. Also ensured the breadcrumbs were all consistent.

Made the block of breadcrumbs to be a <nav id="breadcrumbs"
aria-label="Breadcrumb" class="breadcrumbs"> with an ordered list
inside. The last breadcrumb also has aria-current="page" to specify that
it is the current page.

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)

- Confirm that OPAC templates are updated consistently to use
  breadcrumbs markup beginning with '<nav
  id="breadcrumbs" aria-label="Breadcrumb" class="breadcrumb">'
- Pages in the OPAC should look consistent, with the last breadcrumb
  styled as text and with the "aria-current" attribute "page."

Sponsored-by: Catalyst IT
Signed-off-by: Henry Bolshaw <bolshawh@parliament.uk>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>