Add Bookmark.display_name, just like Album.

etiquette/objects.py

@@ -639,6 +639,13 @@ class Bookmark(ObjectBase):
         self._uncache()
         self.deleted = True
 
+    @property
+    def display_name(self):
+        if self.title:
+            return self.title
+        else:
+            return self.id
+
     @decorators.required_feature('bookmark.edit')
     @decorators.transaction
     def edit(self, title=None, url=None):

frontends/etiquette_flask/templates/bookmarks.html

@@ -58,11 +58,7 @@
                 data-editor-placeholder="title (optional)"
                 data-editor-empty-text="{{bookmark.id}}"
                 >
-                    {%- if bookmark.title -%}
-                        {{bookmark.title}}
-                    {%- else -%}
-                        {{bookmark.id}}
-                    {%- endif -%}
+                    {{-bookmark.display_name-}}
                 </a>
 
                 <a