Support whitelist of parameters in interactive mode

[stefk]

This PR adds a feature very similar to the one discussed and proposed in #83 and #93, but takes a whitelist approach instead. The idea is to allow to specify which parameters are asked in interactive mode, and let the handler use the default/dist values otherwise:

{
    "extra": {
        "incenteev-parameters": {
            "interactive-keys": [
                "param_1",
                "param_3",
                "param_8"
            ]
        }
    }
}

[ingowalther]

Hello,

is this PR going to me merged?

Greets Ingo