Revert "ontology: Remove tracker:writeback property from nao:prefLabel"
Revert "ontology: Remove tracker:writeback property from nao:prefLabel"

This reverts commit 9dcee2bdc0ef2beb9be83b31180c18fb2c0ecfbd.

Tracker-extract won't trigger anymore a writeback petition when inserting
tags. So, even if it doesn't work yet as expected, is not harmful in normal
operations.

hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker