delete groups

Whoops, forgot to add this functionality earlier.

- allow owner to delete a group
- change all group lists to closed curation with group=False when group deleted

bookwyrm/templates/groups/delete_group_modal.html

@@ -8,14 +8,14 @@
 {% endblock %}
 
 {% block modal-footer %}
-    <div>
-        {% csrf_token %}
-        <input type="hidden" name="id" value="{{ group.id }}">
-        <button class="button is-danger" type="submit">
-            {% trans "Delete" %}
-        </button>
-        {% trans "Cancel" as button_text %}
-        {% include 'snippets/toggle/toggle_button.html' with text=button_text controls_text="delete_list" controls_uid=list.id %}
-    </div>
+<form name="delete-group-{{ group.id }}" action="{% url 'delete-group' group.id %}" method="POST">
+    {% csrf_token %}
+    <input type="hidden" name="id" value="{{ group.id }}">
+    <button class="button is-danger" type="submit">
+        {% trans "Delete" %}
+    </button>
+    {% trans "Cancel" as button_text %}
+    {% include 'snippets/toggle/toggle_button.html' with text=button_text controls_text="delete_group" controls_uid=group.id %}
+</form>
 {% endblock %}