onFinishChange(fnc) {
        this.__onFinishChange = fnc;
        return this;
      }
Specify that a function fire every time someone "finishes" changing
the value wih this Controller. Useful for values that change
incrementally like numbers or strings.

@param {Function} fnc This function will be called whenever
someone "finishes" changing the value via this Controller.
@returns {dat.controllers.Controller} this