Coerce the default data to strings to avoid exceptions

debexpo/templates/plugins/default/html.mako

 <div class="qa-header">
-${o.from_plugin}: ${o.outcome}
+${o.from_plugin}: ${str(o.outcome)}
 </div>
+%if o.rich_data:
 <div class="qa-content">
-${h.converters.nl2br(o.rich_data)}
+${h.converters.nl2br(str(o.rich_data))}
 </div>
+%endif

debexpo/templates/plugins/default/text.mako

-${o.rich_data}
+${str(o.rich_data)}