flat.LCD flattens a list of Lebesgue decomposed distributions given through ...,
i.e., it takes all list elements and mixing coefficients and builds up the mixed
distribution (forgetting about the components); the result will be one distribution of
class UnivarLebDecDistribution. If mixCoeff is missing, all list elements
are equally weighted. It is used internally in our methods for "*", "/",
"^" (see operators-methods),
Minimum, and convpow, as well in method flat.mix.