Multi-Objective Bayesian Optimization

New Features

• Multi-Objective Acquisition Functions (#466)
  • q-Expected Hypervolume Improvement
  • q-ParEGO
  • Analytic Expected Hypervolume Improvement with auto-differentiation
• Multi-Objective Utilities (#466)
  • Pareto Computation
  • Hypervolume Calculation
  • Box Decomposition algorithm
• Multi-Objective Test Functions (#466)
  • Suite of synthetic test functions for multi-objective, constrained
    optimzation
• Multi-Objective Tutorial (#468)
• Abstract ConstrainedBaseTestProblem (#454)
• Add optimize_acqf_list method for sequentially, greedily optimizing 1 candidate
  from each provided acquisition function (d10aec9)

Bug fixes

• Fixed re-arranging mean in MultiTask multi-output models (#450).

Other changes

• Move gpt_posterior_settings into models.utils (#449)
• Allow specifications of batch dims to collapse in samplers (#457)
• Remove outcome transform before model-fitting for sequential model fitting
  in multi-output models (#458)