Create GML for AQD Stations

[thijsbrentjens]

Separate issue, part of #7.

For Stations, the XML schemas define a type AQD_StationType. This is an extension of EF's ef:EnvironmentalMonitoringFacilityType

See XSD.

So there is more than EF only to provide.

[thijsbrentjens]

Just has encoded data conforming to the AQD already. See issue #7 for the details.

There are examples for Dataflow D on the AQD portal as well, e.g.: http://cdr.eionet.europa.eu/nl/eu/aqd/d/envu9_j7q/REP_D-NL_RIVM_20140805_D-002.xml as found on the EIONET repository http://www.eionet.europa.eu/aqportal/Drep1