Fix broken links on template statistics page

Tests assumed that the API returns the template `id` as part of the
object. It doesn’t – it returns it as the key used to look up the
object. The `id` was missing from the transformation into the format
used by the front end.

For some reason Flask is fine building the URL with `template_id=None`,
but obviously this doesn’t generate a valid link.

tests/app/main/views/test_dashboard.py

@@ -649,11 +649,13 @@ def test_format_template_stats_to_list():
         'counts': counts,
         'name': 'foo',
         'requested_count': 7,
+        'id': 'template_1_id',
     } in stats_list
     assert {
         'counts': {},
         'name': 'bar',
         'requested_count': 0,
+        'id': 'template_2_id',
     } in stats_list