Configurable key signature playback

Hi all,

This feature would probably be more of an overhaul, but it would be very useful for things like maqam music, and would unlock the potential of all those currently decorative accidentals.

The first part is to separate the displayed key signature from the played key signature, as is possible with time signatures. In the master palette, a time signature that effects 3/4 but displays 19/7 can be created, and bars can be assigned their own 'Actual' durations without needing a time signature change. Applying this to key signatures, it would be possible to have a displayed key signature of { B flat + E flat + A flat + D half-flat } (C bayati), but have the playback key set to { B flat + E flat + A flat } instead of all naturals.

The second part is to enable new key signature playback definitions, rather than just the 15 default ones. This way, I could make a key signature like { B flat + F sharp + E flat } and set it to playback the same key signature, which would make a lot of transcriptions easier.

The third part involves making the micro-tonal tuning functionality part of the key signature playback. Ideally there would still be an additional micro-tuning tuning option for individual notes, which would be added to the values stored in the key signature. Removing the 200 cents limit would be useful too, for things like triple-sharps which are hard to implement at the moment. This part would help with all sorts of non-12-TET temperament playback.

The fourth part gives purpose to the decorative accidentals. The function of an accidental would be defined within the key signature playback setting for any given key signature, so people would be free to add and use their own.

Thanks for reading :)