Consider additional GML adapters

[cdmgtri]

Feedback from issue #101 (Harmonize location area elements and GML adapters).

I was wondering if we could discuss nc:AreaRegionAbstract, m:Location AugmentationType, and approach regarding GML in general. Since ISO and OGC have resource to sustain these classes, I was curious as to whether or not we could bring all of the feature classes together under a common namespace and have someone/some group sustaining the connections to GML. I see nc, mo, geo domains all touching GML to some extent.

[DonClysdale]

In xsd/external/have/geo-oasis.xsd and xsd/external/have/gml-oasis.xsd the namespace prefix gml is defined as xmlns:gml="http://www.opengis.net/gml" while in the /xsd/external/ogc/gml/3.2.1/*.xsd schema the gml namespace prefix is defined as xmlns:gml="http://www.opengis.net/gml/3.2".

It would be good to standardize on the "http://www.opengis.net/gml/3.2" namespace if both schema are meant to derive from the same base types. However there are some duplication of element and type names between have/.xsd and ogc/gml/3.2.1/.xsd schema (e.g. gml:Point and gml:PointType) which do not have identical definitions - so perhaps the target namespace and prefix for elements in the xsd/external/have/gml-oasis.xsd should be renamed similar to the urn in the target namespace for xsd/external/have/geo-oasis.xsd.

[cdmgtri]

The NTAC has confirmed that we cannot make changes to the HAVE external schemas so we cannot do anything about their use of a different set of GML schemas.

Separately, the NTAC is working on creating a profile of NIEM's GML external schemas to only include the content used by NIEM adapters. Users who wish to reuse other parts of GML may replace the NIEM profile with their own.