Create a plot with the beta sampled from its distribution, as a function of context-level feature $W$. Only works for the hierarchical model (hdpGLM), not the dpGLM
plot_beta_sim(data, w.idx, ncol = NULL)the output of the function hdpGLM_simulateData
integer, the index of the context level covariate the plot
integer, the number of columns in the grid of the plot