Core: Eliminate the use of QDir

Use POSIX functions instead, in not-Windows.
Core: Eliminate the use of QSettings

The new code is not a drop-in replacement in OS X: the config file now
has the same kind-of-ini format as in Linux, and it's expected to be at
~/Library/Application Support/VapourSynth/vapoursynth.conf
wscript: No more Qt
Core: Use thread-safe readdir_r in not-Windows
Core: Move the config parser to settings.cpp
Merge pull request #61 from dubhater/less_qt

No more Qt in unwindows