allow several `biblScope` elements within `bibl` (within `desc`, inside `interp`)

[timofruehwirth]

it would be good if bibl can contain multiple biblScope elements, eg doc 0031:

                           <bibl>
                              <author ref="acdh:amp-index-persons.xml#amp_person_2"/>
                              <title level="a">Die zwei Welten des W. H. Auden: Auf den Spuren des englischen Poeten in Kirchstetten</title>
                              <title level="j">morgen</title>
                              <pubPlace ref="acdh:amp-index-places.xml#amp_place_id_10"/>
                              <date when-iso="1977"/>
                              <biblScope unit="volume">1</biblScope>
                              <biblScope unit="page" from="6" to="12"/>
                           </bibl>

[timofruehwirth]

thank you, works now