A few changes necessary to run a realistic model of the south illuminators

[orelgueta]

Two changes implemented here,

• The schema validation failed when I tried setting

  flasher_pulse_shape:
        version: "2.0.0"
        value: ["Gauss-Exponential", 0.1699, 1.8398]
        unit: [null, ns, ns]
        model_parameter_schema_version: "0.2.0"
  

  even though the code should support this. Either way, I don't think so many changes are actually necessary to get it to work. I will try reducing them before making this a real PR.
• The Gauss-Exponential was only supported for the flasher, not for illuminators. That I modified in this PR.