GEOT-4468 added partial support for custom outputFormat in WFS 1.1.0 DataStore

Added support for custom outputFormat for WFS 1.1.0 DataStore using a new connection datastore parameter.
This can be used to force a GetFeature request to ask for GML2 response.
To ease parsing of GML2 responses support for both posList and coordinates has been enabled for coordinate lists.
Support for MultiCurve elements with LineString members for GML3 has been added too.