Bug 27610: (follow-up) Hide <h1> on opac-main.tt

This patch visually hides the <h1> on opac-main.tt so that libraries' customisations of their home pages are not disturbed by the introduction of a descriptive <h1>, but the heading is still available to be read out by screenreaders in the summary of headings on the page.

Test plan:

1) Apply dependencies and all patches on this bug report
3) Ensure the <h1> "Koha home" heading on the OPAC main/home page is hidden visually, but in the source code you can see it

Sponsored-by: Catalyst IT
Signed-off-by: Henry Bolshaw <bolshawh@parliament.uk>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>

koha-tmpl/opac-tmpl/bootstrap/en/modules/opac-main.tt

@@ -66,7 +66,7 @@
             <div class="col order-md-1 maincontent">
         [% END %]
 
-        <h1>Home</h1>
+        <h1 class="sr-only">Koha home</h1>
 
         [% IF Koha.Preference( 'OpacNewsLibrarySelect' ) %]
             [% UNLESS news_item %]