Rename "Transferred" to "Direct Transfer"

The rationale for this naming choice has been discussed in issue #1299

ihatemoney/templates/statistics.html

@@ -10,7 +10,7 @@
         <th class="d-md-none">{{ _("Who?") }}</th>
         <th>{{ _("Paid") }}</th>
         <th>{{ _("Expenses") }}</th>
-        <th>{{ _("Transferred") }}</th>
+        <th>{{ _("Direct transfer") }}</th>
         <th>{{ _("Received") }}</th>
       </tr>
     </thead>