Response stage definitions

[Jollyfant]

Currently it appears that response stages are given as objects:

[{
  "poleszeros": {
    "pzTransferFunctionType": DIGITAL (RADIANS/SECOND)
  }
}, {
  "coefficients": {
    "cfTransferFunctionType": ANALOG (RADIANS/SECOND)
  }
}]

I propose to move the response stage identifier (i.e. poleszeros & coefficients) as a type:

[{
  "responseType": "poleszeros",
  "pzTransferFunctionType": DIGITAL (RADIANDS/SECOND)
}, {
  "responseType": "coefficients",
  "cfTransferFunctionType": ANALOG (RADIANS/SECOND)
}]

Thoughts? @crotwell