add topic sorting & js to support it

app/templates/mod/panel.html

@@ -1,4 +1,4 @@
-{%- from 'common/macros.html' import subheader, babycode_editor_component -%}
+{%- from 'common/macros.html' import subheader, babycode_editor_component, sortable_list, sortable_list_item -%}
 {%- extends 'base.html' -%}
 {%- block title -%}settings{%- endblock -%}
 {%- block content -%}
@@ -19,5 +19,18 @@
 </fieldset>
 <fieldset class="plank" id="sort-topics">
   <legend>Sort topics</legend>
+  <p>Drag topics around to reorder them. Press "Save order" when done.</p>
+  <form method="POST" action="{{url_for('mod.sort_topics')}}">
+  <input type="submit" value="Save order">
+  {%- call() sortable_list() -%}
+    {%- for topic in topics -%}
+      {%- call() sortable_list_item(key="topics") -%}
+        <h2 class="info">{{ topic.name }}</h2>
+        <div>{{topic.description}}</div>
+        <input type="hidden" name="topics[]" value="{{ topic.id }}">
+      {%- endcall -%}
+    {%- endfor -%}
+  {%- endcall -%}
+  </form>
 </fieldset>
 {%- endblock -%}