fix: correct inverse property name to reverse_name

this makes it consistent with the assumptiopn in models.py
that the inverse is saved under the attribute reverse_name

TODO: like subj_model and obj_model, can we mandate these fields in the
base class to avoid confusion?

apis_core/relations/templates/templatetags/relations_links.html

@@ -19,7 +19,7 @@
     <button type="button" class="btn btn-sm">
 
       {% if rel in relation_types_reverse %}
-        {{ model.name_reverse }}
+        {{ model.reverse_name }}
       {% else %}
         {{ model.name }}
       {% endif %}