Show "More by" on author page

Uses Goodread's list of author's books, filtering out the books that are already in the user's library.

Requires the Goodreads dependency and API information.

cps/templates/author.html

@@ -64,7 +64,7 @@
   </div>
 </div>
 
-{% if other_books is not none %}
+{% if other_books %}
 <div class="discover">
   <h3>{{_("More by")}} {{ author.name|safe }}</h3>
   <div class="row">