This is a messy commit, because the "qPref" system relies
heavily on QString, which means lots of conversions between
the two worlds. Ultimately, I plan to base the preferences
system on std::string and only convert to QString when
pushing through Qt's property system or when writing into
Qt's settings.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
