Minor improvements and publication functions

• removed ties_pred from models that do not have ties and from the stan models.
• fixed predict for models with ties, so we return a vector y_pred with 0, 1, 2 and not separate as now
• removed posterior distributions from the get_rank_of_players and get_probabilities. Now we have new functions to obtain the data frame or the posterior distributions separately. The posterior is now returned as matrix
• Probabilities table is now optional in the summary function
• New functions to get the probabilities for specific data get_probabilities_newdata_df and get_probabilities_newdata_posterior
• Publication ready functions for
  • plots: get_parameters_plot function and a thin S3 plot wrapper for the same function. Plots are default to APA.
  • tables: Functions for publication tables: get_parameter_table, get_probabilities_table and get_rank_of_players_table
• get_hpdi_parameters became get_parameters and the user specify if credible intervals or hpdi
• Added ties to expand_aggregated_data.
• We can get now both credible and HPD intervals in get_parameters. n_eff and Rhat are also now possible to add and remove from this df
• Added functions to save and load bpc models