WebSearch: enable full search result for of=id

* Enables the search API to return a full result when using the
  "id" output format which is useful when querying. It does
  this by ignoring CFG_WEBSEARCH_MAX_RECORDS_IN_GROUPS if output
  format is "id".

This will allow this kind of query to actually provide useful results:

```python
from invenio.invenio_connector import InvenioConnector

inspire = InvenioConnector(url="http://inspirehep.net")
res = inspire.search(p="ellis", of="id", rg=10000000)
```
With this patch `len(res)` will return 3000+ results instead of 251 which `CFG_WEBSEARCH_MAX_RECORDS_IN_GROUPS` is currently set to.