Implement algorithmically efficient solutions for EHVI

[iraikov]

EHVI = Expected Hypervolume Improvement

References:
Efficient Computation of Expected Hypervolume Improvement Using Box Decomposition Algorithms. https://arxiv.org/pdf/1904.12672.pdf
Efficient computation of the search region in multi-objective optimization. EJOR 2017.
A Box Decomposition Algorithm to Compute the Hypervolume Indicator. https://arxiv.org/abs/1510.01963