some changes for topics many-to-many relationship

- iameta.pl adds topic and adds it to the IA topic relationship

test this with
```
cd
curl -o ddgc/cache/all_meta.json "https://russell2.duckduckgo.com/metadata106.json"
script/iameta.pl
```

 lines 29-35 need to be uncommented and comitted after tests (see TODO)

- uses the topic relationship in JSON endpoints
- removes some old code used for xslate version

@MariagraziaAlastra 
```perl
$new_ia->topics->find($topic->id) or $new_ia->add_to_topics($topic);
```

I don't think upsert accessors are created for relationships.