InstantAnswer.pm: Add template attribute.

I was thinking that we should probably add the `template` attribute in the JSON output. Queries such as `/ia/json/template/text` work, but it's not in the JSON.

We could use this:
- To display the template name on the page.
- To display the template name on the index.

@russellholt @jbarrett @MariagraziaAlastra @jdorweiler my question is how is this generated? How does it deal with custom templates such as currency? (https://duckduckgo.com/?q=usd+to+php)