Support WFS 2.0 response paging

[florianesser]

WFS 2.0.0/2.0.2 servers can support response paging by providing a URI in the next attribute of the returned wfs:FeatureCollection (see sec. 7.7.4.4 in the WFS 2.0 standard). The provided URI may be used by the client to retrieve the following set of results. If the server supports the feature, using the URI from next can also allow transaction-safe result set iteration.

Implementation notes:

• Tests with Geoserver indicate that in order for a WFS to add the next attribute to the response, it may be required to add &STARTINDEX=0 in addition to the COUNT parameter, although the standard says that only COUNT should be required to activate response paging (compare the response of this request to this)