behavior of virtual instruments when # notes < # hardware instruments

[drsm79]

Various possibilities to support:

• unison - lowest note wins (e.g. I1, I3 play N1, I2 plays N2)
• unison - highest note wins (e.g. I1 plays N1, I2, I3 play N2)
• drop - I1 plays N1, I2 plays N2, I3 is silent (current behaviour after Virtual hardware instruments #41 is committed)
• something with shifts?