XSL utility / Add function to retrieve thesaurus URI

RDF based schema plugins may need the URI of vocabularies in a number of places. This utility is used in the DCAT-AP plugin when building concept elements in thesaurus-transformation.xsl:

eg.
```
  <dct:accessRights xmlns:dct="http://purl.org/dc/terms/">
    <skos:Concept xmlns:skos="http://www.w3.org/2004/02/skos/core#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" rdf:about="http://publications.europa.eu/resource/authority/access-right/PUBLIC">
      <skos:prefLabel xml:lang="en">public</skos:prefLabel>
      <skos:prefLabel xml:lang="es">public</skos:prefLabel>
      <skos:inScheme rdf:resource="http://publications.europa.eu/resource/authority/access-right" />
    </skos:Concept>
  </dct:accessRights>
```

core/src/main/java/org/fao/geonet/util/XslUtil.java

@@ -1440,7 +1440,7 @@ public static String getThesaurusIdByTitle(String title) {
 
         return thesaurus == null ? "" : "geonetwork.thesaurus." + thesaurus.getKey();
     }
-    
+
     /**
      * Retrieve the thesaurus title using the thesaurus key.
      *
@@ -1455,6 +1455,15 @@ public static String getThesaurusTitleByKey(String id) {
     }
 
 
+    public static String getThesaurusUriByKey(String id) {
+        ApplicationContext applicationContext = ApplicationContextHolder.get();
+        ThesaurusManager thesaurusManager = applicationContext.getBean(ThesaurusManager.class);
+        Thesaurus thesaurus = thesaurusManager.getThesaurusByName(id);
+        return thesaurus == null ? "" : thesaurus.getDefaultNamespace();
+    }
+
+
+
     /**
      * Utility method to retrieve the name (label) for an iso language using it's code for a specific language.
      * <p>
@@ -1594,7 +1603,7 @@ private static List<Element> buildRecordLink(List<Hit> hits, String type) {
     public static String escapeForJson(String value) {
         return StringEscapeUtils.escapeJson(value);
     }
-  
+
     public static String getWebAnalyticsService() {
         ApplicationContext applicationContext = ApplicationContextHolder.get();
         WebAnalyticsConfiguration webAnalyticsConfiguration = applicationContext.getBean(WebAnalyticsConfiguration.class);