Greatly simplified algorithmic code of the OWL exporter class
Fourth and last batch of major code overhaul

Removed all `using namespace ...` instances to make the code less namespace-pollutant (and less polluted). All `for` loops were replaced by their respective `simpler` versions where applicable (so iterators are only used explicitly when `erase` was actually used on lists).

Nicified lots of smaller code bits as well, making the overall code more readable.