Implement creation of PseudoExpectation constraints and PseudoExpectation variables

[blegat]

[chriscoey]

are there any alternative names, names that sound more kind of "parallel" to "sum of squares polynomials"? it's pretty unobvious that "pseudoexpectations" are related via duality to "sums of squares". not a big deal if not.

[blegat]

All the names I know are "pseudo-expectations" and "Lasserre moment series"