Modify Links model to generate GetCapabilities links for WMS, WFS, WCS 

__What does this PR do?__

Changes Link instances created in geoserver_post_save to add URLs for valid GetCapabilities requests instead of the generic /geoserver/wms and /geoserver/wfs URLs that were used previously.  Also removes the 'OWS' name Link from the link set associated with a ResourceBase and updates the ResourceBase.get_ows_url() to return the WMS GetCapabilties link instead.

Updates the template full_metadata.xml in catalogue app so that  ISO XML responses will include these links (in addition to the 'data' and 'image' type links it already does).  This is useful for downstream clients of the CS-W service to be able to recognize and provide better representation of resources in GeoNode.
i.e. 

```
<gmd:protocol>
 <gco:CharacterString>{{link.link_type}}</gco:CharacterString>
```