Fixed several portability issues regarding endianness:
- introduced QSynth::convertSamplesFromNativeEndian() method to simplify conversion of samples produced by Synth to an arbitrary byte order
- AudioFileWriter now ensures .wav files being written in little endian as required
- for consistency with mt32emu_smf2wav, AudioFileWriter now writes .raw files in big endian
- changed little endian audio formats to native endian in some audio drivers