Bug 18665 - Translatability: Add tt filter to allow html tags inside tt directives

HTML tags inside template toolkit directives are not allowed because of translation issues.
Add a filter that handles HTML tags.

Note you need to write quotes ' around the text you want displayed as a
heading

To test:
- Apply patch
- Add [% USE HtmlTags %] to the top of a tt file
- Add something like [% 'My nice title' | $HtmlTags tag="h1" %] to the tt file
- Verify that in output 'My nice title' has h1 tags
- Change template directive to something like
  [% 'My nice title' | $HtmlTags tag="h1" attributes='title="This is a nice title attribute"' %]
- Verify that title attribute displays in output (source code or tooltip on 'My nice title')

Notes: - Tests are planned for a second patch
       - Update for Wiki coding guidelines

Signed-off-by: Alex Buckley <alexbuckley@catalyst.net.nz>

Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>

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

Koha/Template/Plugin/HtmlTags.pm

@@ -0,0 +1,40 @@
+package Koha::Template::Plugin::HtmlTags;
+
+# Copyright Marc Véron / marc veron ag, Switzerland
+
+# This file is part of Koha.
+#
+# Koha is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# Koha is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Koha; if not, see <http://www.gnu.org/licenses>.
+
+use Modern::Perl;
+
+use Template::Plugin::Filter;
+use base qw( Template::Plugin::Filter );
+
+our $DYNAMIC = 1;
+
+sub filter {
+    my ( $self, $text, $args, $config ) = @_;
+    return "" unless $text;
+    return $text unless $config->{tag};
+    $config->{attributes} //= '';
+
+    if ( $config->{attributes} ) {
+        return '<' . $config->{tag} . ' ' . $config->{attributes} . '>' . $text . '</' . $config->{tag} . '>';
+    } else {
+        return '<' . $config->{tag} . '>' . $text . '</' . $config->{tag} . '>';
+    }
+}
+
+1;