Need 'id' attribute in element 'infraAttributes'

Element infraAttrGroups needs no id attribute, because it has only a grouping function.

Element infraAttributes needs an id attribute for referencing in track elements with attribute infraAttrGroupRef.

Currently it looks like:

    <rail:infraAttrGroups id="iag1">
        <rail:infraAttributes>
            <rail:gauge value="1435"/>
        </rail:infraAttributes>
        <rail:infraAttributes>
            <rail:gauge value="1600"/>
        </rail:infraAttributes>
    </rail:infraAttrGroups>

'''Currently there is no possibility to use different infrastructure attribute groups!!!

There is no possibility to extend element infraAttributes with a "foreign id attribute", because there is no anyAttributes allowed.