workflows: result templating

* Amends result rendering to use templates
  under the folder templates/workflows/results.

* fixes refextract task.

* Adds refextract template.

* Adds fulltext_download template.

Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>
To avoid a possible `AttributeError` here you can check using `hasattr`: 
```
if hasattr(result, "to_dict"):
      result = result.to_dict()
else:
      result_list.append(result)
```
However, the best would be to write an update script and this check would not be needed. I can help you with that.