Replace TrackerDomainOntology class with a simpler function
This allows us to remove some code from libtracker-miners-common, but the motivation is actually to fix a name conflict between libtracker-common and libtracker-miners-common.
Previously we were prevented from linking statically to libtracker-miner, and prevented from using link-time optimization, due to the duplicate GTypes.
The code is now diverged from that in libtracker-common, but it's unlikely to see major changes because the "domain ontology" format is part of Tracker's public API.
Fixes: tracker#116 (closed)