Adding support to fulltext and ngram index definitions in mappings.xml.

    The XCQL2Xpath Stylesheet now interprets constructs like the following:
        <index key="myFulltextIndex" index-type="fulltext"/>
        <index key="myNgramIndex" index-type="ngram"/>

    These are translated into:
        myIndexPath[ft:query(.,$term)]
        myIndexPath[ngram:contains(.,$term)]