Allow pages to be ordered with PCDM sets

[mark-dce]

For text works, we have attached pages as unordered PCDM files since the TEI transcript provides the ordering for the viewer.

If WUSTL wants full PDCM interoperability, we would need to add ordering within a PCDM container. This has both performance and IU implications that would need to be scoped and worked through.

[jcoyne]

That's almost correct. PCDM provides both ordered and unordered file members. It is up to us to choose which way we want to do it. When Trey is done with his work, the performance difference should be very slight (and much improved from the current way).