DHLAB web API supports more params than the python wrappers

[iciclejj]

The functions in dhlab/api/dhlab_api.py don't allow all the parameters that the web API allows. Is this intended?

The web API is documented at http://api.nb.no/dhlab/.

[iciclejj]

For example, /get_metadata supports both dhlabids and urns, while get_metadata in dhlab/api/dhlab_api.py only allows urns.

[iciclejj]

Relevant: #162