Use reverse lookups for urls

bookwyrm/templates/book/edit_book.html

@@ -239,7 +239,7 @@
     {% if not confirm_mode %}
     <div class="block">
         <button class="button is-primary" type="submit">{% trans "Save" %}</button>
-        <a class="button" href="/book/{{ book.id }}">{% trans "Cancel" %}</a>
+        <a class="button" href="{{ book.local_path}}">{% trans "Cancel" %}</a>
     </div>
     {% endif %}
 </form>

bookwyrm/templates/book/editions.html

@@ -15,14 +15,14 @@
     {% for book in editions %}
     <div class="columns is-gapless mb-6">
         <div class="column is-cover">
-            <a href="/book/{{ book.id }}">
+            <a href="{{ book.local_path }}">
                 {% include 'snippets/book_cover.html' with book=book cover_class='is-w-m is-h-m align to-l-mobile' %}
             </a>
         </div>
 
         <div class="column my-3-mobile ml-3-tablet mr-auto">
             <h2 class="title is-5 mb-1">
-                <a href="/book/{{ book.id }}" class="has-text-black">
+                <a href="{{ book.local_path }}" class="has-text-black">
                     {{ book.title }}
                 </a>
             </h2>