Create WFS Links for WMS remote layers that have WFS support

[giohappy]

For remote layers that support WFS, we want the GeoNode client to show the filtering and attribute table functionality.

The GeoNode client checks the presence of an OGC:WFS Link inside the dataset API response to enable the related tools.
This link is never generated for remote WMS lsyers.
A more check will be added to harvesters to perform an OGC DescribeLayer request if available (OpenGIS Styled Layer Descriptor Profile of the Web Map Service Implementation Specification). When the request is available and a valid response is returned, the owsType will be parsed. In case it contains the wfs string, an OGC:WFS Link for the remote dataset will be created.