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