Implement and use Author.display_name

fedireads/templates/snippets/shelf.html

@@ -42,7 +42,7 @@
         <a href="/book/{{ book.id }}">{{ book.title }}</a>
     </td>
     <td>
-        {{ book.authors.first.name }}
+        {{ book.authors.first.display_name }}
     </td>
     <td>
         {% if book.first_published_date %}{{ book.first_published_date }}{% endif %}