Improve handling of GML geometries with references

In sophisticated GML encodings, geometries can contain references to other geometry parts, e.g.:

```xml
<aixm:Surface gml:id="uuid.04a4c778-213c-4a94-bd92-185707978b2b.2014-04-03.5" srsName="urn:ogc:def:crs:EPSG::4326">
  <gml:patches>
    <gml:PolygonPatch>
      <gml:exterior>
        <gml:LinearRing>
          <gml:pos>60.83361053466797 25.762222290039062</gml:pos>
          <gml:pos>60.81916809082031 25.905277252197266</gml:pos>
          <gml:pos>60.705833435058594 26.2147216796875</gml:pos>
          <gml:pos>60.67805480957031 26.29138946533203</gml:pos>
          <gml:pos>60.47027587890625 26.220277786254883</gml:pos>
          <gml:pos>60.592498779296875 25.991945266723633</gml:pos>
          <gml:pointProperty xlink:href="urn:uuid:d646ea22-2c72-454c-aea2-7c0dd376b8ea"/>
          <gml:pos>60.692222595214844 25.691110610961914</gml:pos>
          <gml:pos>60.83361053466797 25.762222290039062</gml:pos>
        </gml:LinearRing>
      </gml:exterior>
    </gml:PolygonPatch>
  </gml:patches>
</aixm:Surface>
```
This patch does the following:

* Parsed geometry properties inside geometries respect the configured GMLReferenceResolver
* Inserts into the SQLFeatureStore do not fail if envelope for a feature can not be calculated due to geometry reference issues. Instead, a NULL envelope is used.