Kazoo 2460: CDRs chunking

I think this should be:

```
case cb_context:fetch(...) of
    'true' ->
        cowboy_req:chunk(<<",", (wh_json:encode(CDR)/binary>>, Req),
        normalize_and_send('json', JObjs, {Req, Context});
    _Else ->
        cowboy_req:chunk(wh_json:encode(CDR), Req),
        normalize_and_send('json', JObjs, {Req, cb_context:store(Context, 'started_chunk', 'true')})
end
```
Then you're not doing the `store/3` over and over for no reason.
end
```