Renaming functions and classes

[dc-luo]

Main purpose of this PR is to make naming changes for style and clarity.

Cost functionals now have their consistently named methods: costGrad to grad, costHessian to hessian

Changed MeanVarRiskMeasure to MeanVarRiskMeasureStochastic to indicate it is the stochastic approximation version

By default, we now assume SAA risk measures support MPI based sample parallelism

• Deprecated the original MeanVarRiskMeasureSAA, which was a purely serial implementation of sample average approximation for the mean variance risk measure
• Renamed MeanVarRiskMeasureSAA_MPI to MeanVarRiskMeasureSAA
• Renamed SuperquantileRiskMeasureSAA_MPI to SuperquantileRiskMeasureSAA
• Their setting functions also had respective name changes

Some utilities also had name changes to snake case for stylistic reasons

• gatherSamples to gather_samples
• sampleSuperquantile to sample_superquantile (and similar)
• applyBC to apply_BC, homogenizeBC to homogenize_BC

Note: functions that are also in hIPPYlib as camel case are not changed to snake case.

Examples have been updated with new capabilities

• NewtonCG example with poisson
• Comparison of deterministic and OUU for hyperelasticity material design