Build improvement:
- introduced build options munt_WITH_MT32EMU_SMF2WAV and munt_WITH_MT32EMU_QT to control build of subcomponents
- renamed build option WITH_INTERNAL_PORTAUDIO -> munt_WITH_INTERNAL_PORTAUDIO for consistency
- added build option mt32emu-qt_WITH_ALSA_MIDI_DRIVER to control whether to use ALSA MIDI driver (if enabled, ALSA MIDI sequencer ABI is used to communicate with other applications, if disabled, ALSA/OSS4 raw MIDI ports and OSS sequencer ABI are available)
- OSS MIDI driver no longer compiles if it isn't needed