Beta distribution (Guassian/gauss distribution) in random selection on a ValueRange

Notes:

• Gaussian distribution is not immediately compatible with nullable=true. The ValueSelector will need to configure a probability for the value null.
• Gaussian distribution is not immediately compatible with a composite value range. The ValueSelector will need to configure a probability for each child value range.
• Gaussian distribution requires the current value of the variable as a parameter to know where to centralize the bell curve (= set the mean)
• Gaussian distribution has many parameters (mean, standard deviation) that all need to be tweakable

Therefore, the Gaussian distribution is not build into the interface ValueRange, but the ValueSelector will need to recognize the IntValueRange instance and do it's work.