Completely empty measures should be filled by a single ghost rest of a whole

[ciacob]

Completely empty measures should be filled by a single ghost rest of a whole. Currently they are filled by rests totaling to the measures nominal duration, e.g., for a measure having the time signature of 3/8, on eighth and one fourth ghost rests are added. According to music theory, a single whole (ghost) rest would be preferable.

Attachment shows a piece of code that was removed from QueryEngine.as, which aimed to mitigate the issue, namely by allowing the user to manually enter a whole rest into the measure, that would mean "the nominal duration of this measure". However, this solution was breaking the (already fragile) abc2ps layout engine.