Prefer flats rather than sharps when converting from MIDI

Prefer flats rather than sharps when converting from MIDI

It's ambiguous before we look at the key, (which often tells us what
to do). But when the key doesn't indicate, we can really say flat from
above or sharp from below.

The preference for choosing flat here is so that if we input a scale
such as Db major, we get that key signature (with 5 flats) rather than
the rather unlikely key of C# with 7 sharps.