Missing estimation option: posterior_sampling_method

Only use_tarb is specified under MH_options. The location of TaRB options is also misspecified pointing to: options_.TaRB - the same features are now listed under options_.posterior_sampler_options.

Solution: delete use_tarb checkbox and replace with popup window, naming the option posterior_sampling_method and including the following values: random_walk_metropolis_hastings (default), tailored_random_block_metropolis_hastings, independent_metropolis_hastings, slice.

Also, delete TarB related feature mapping in command_option_mapping.m, namely: tarb_new_block_probability, tarb_mode_compute. This should be changed for sampling_opt with name-value pairs as input taking care of the missing posterior_sampler_options in issue #11 (closed).