feat: add slides translation for search result content type label

Fallback to `btn_slides` translation for language packs which don't yet have a `slides` translation.

Close #1716

i18n/en.yaml

@@ -188,7 +188,7 @@
 - id: open_project_site
   translation: Go to Project Site
 
-# Default titles for archive pages
+# Content types for default archive page titles and search results
 
 - id: posts
   translation: Posts
@@ -202,6 +202,9 @@
 - id: projects
   translation: Projects
 
+- id: slides
+  translation: Slides
+
 # Search
 
 - id: search

layouts/partials/site_js.html

@@ -61,7 +61,8 @@
         'post': {{ i18n "posts" }},
         'project': {{ i18n "projects" }},
         'publication' : {{ i18n "publications" }},
-        'talk' : {{ i18n "talks" }}
+        'talk' : {{ i18n "talks" }},
+        'slides' : {{ i18n "slides" | default (i18n "btn_slides") }}
         };
     </script>
     {{ end }}