Fix page labeling!

[jechols]

Somehow for the past six years, we've had broken page labeling in NCA. The METS XML template checks for the presence of a page label, and if it is present it adds the page sequence number to the XML. Not the label, the sequence number. This means that most of the time, we have incorrect labels once an issue makes its way to ONI.

The code fix should be trivial, but correcting the past six years' of batches is going to be a massive undertaking. That's not in scope for this issue, just something we will have to figure out. It might make sense to open a new ticket to come up with an NCA standalone script that can find and fix live and archived batches....