make "identifier" attribute true by default in versioned file

Now that I can run tests through to the digitization step thanks to earlier errors being resolved, I now find that digitization unfortunately crashes for our reference Run4 geometry tag...

I believe this is due to handling of the GeoIdentifierTag added in !128 (merged), and so I am hopeful that changing the default value for the associated attribute in the versioned .dtd file will solve this issue similar to the named attribute in !150 (merged)

Adding for comment @dellacqu @mbandier @rbianchi @tsulaia

and for information @tadej @npetters @jmasik @sroe

GeoModelTools/GeoModelXML/GeoModelXml/data/geomodel_v0.dtd

@@ -248,7 +248,7 @@
                      sensitive  IDREF #IMPLIED 
                      alignable  (true|false) "false"
                      named      (true|false) "true"
-                     identifier (true|false) "false"
+                     identifier (true|false) "true"
                      envelope   (true|false) "false"
                      splitLevel CDATA #IMPLIED>