Show slugified version of sponsor display name on dashboard

Fixes #166

Author: mhagander

template/confsponsor/admin_sponsor_details.html

@@ -7,6 +7,10 @@
     <th>Display name:</th>
     <td>{{sponsor.displayname}}</td>
   </tr>
+  <tr>
+    <th>Display name slug:</th>
+    <td>{{sponsor.displayname | slugify}}</td>
+  </tr>
   <tr>
     <th style="vertical-align:top;">Invoice address:</th>
     <td>{{sponsor.invoiceaddr|linebreaks}}</td>