V0.7.4

• Add sampler option algorithm for bolfi-posterior-sampling
• Add a check whether the option given for algorithm is one if the implemented samplers
• Add metropolis sampler algorithm=metropolis for bolfi-posterior-sampling
• Add option warmup to metropolis-sampler
• Add a small test of metropolis-sampler
• Fix bug in plot_discrepancy for more than 6 parameters
• Implement plot_gp for BayesianOptimization classes for plotting discrepancies
  and pair-wise contours in case when we have arbitrary number of parameters
• Fix lint