Track primitive properties ported to C++

[swesterfeld]

I've ported all Track properties to C++ that do not contain object references. Two things are worth mentioning.

1. Const MIDI_MAX_CHANNEL - I declared this as constant, but maybe the definition must be moved elsewhere. It seems to be required in bsebasics.idl, too (there is a // FIXME: MAX_MIDI_CHANNEL in the MidiChannelEvent definition)
2. I didn't touch "signal::property-notify::n-voices" and similar signal code in bsttrackview.cc, I'm not sure what the C++ property equivalent would be

[swesterfeld]

I didn't touch "signal::property-notify::n-voices" and similar signal code

Update: I ported this to C++ now using track.on("notify:n_voices",...) for the new properties.

[tim-janik]

Note, I'm perfectly happy with adding type aliases for complex types, so you don't need to reformat all members. E.g.

using TrackMap = std::map<SfiProxy, Bse::TrackS>;
// other members...
TrackMap    track_map;