groupType expansion should allow different numbers and extra elements

[adcxyz]

groupType expansion should allow for different midiNums of its components,
and for adding more elements to the group:

// different number for polytouch :
(midiNum: [21, 21, 61], groupType: \noteOnOffTouch) 
// -> should expand to 
(
elements: [ 
(midiMsgType: \noteOn, midiNum: 21), 
(midiMsgType: \noteOff, midiNum: 21), 
(midiMsgType: \polyTouch, midiNum: 61)
])

// extra element: 
(midiNum: [21, 21, 61], groupType: \noteOnOffTouch, 
elements: [ (elementType: \led, ioType: \out, midiNum: 42) ]) 
// -> should expand to 
(
elements: [ 
(midiMsgType: \noteOn, midiNum: 21), 
(midiMsgType: \noteOff, midiNum: 21), 
(midiMsgType: \polyTouch, midiNum: 61),
(elementType: \led, ioType: \out, midiNum: 42)
])