message: fixed value distribution
diff: namespace modules {
  namespace commons {
  +class FixedValue : public Distribution {
  + public:
  + FixedValue(const ParamsPtr& params) :
  + Distribution(params),
  + fixed_value_(params->GetListFloat(
  + "FixedValue", "Value always returned when called sample", {1.0f})) {}
  +
  + virtual RandomVariate Sample() {
  + return fixed_value_;
  + }
  +
  + virtual Probability Density(const RandomVariate& variate) const {
  + return 0.0f;
  + };
  +
  + virtual Probability CDF(const RandomVariate& variate) const {
  + return 0.0f;
  + };
  +
  + private:
  + RandomVariate fixed_value_;
  +};
  +
  template<class BoostDistType>
  class BoostDistribution1D : public Distribution {
  