changes defaults, small bugfix in model.py
changes defaults, small bugfix in model.py

 - we change the defaults for batch_size, train_thresh, and
   learning_rate to the values that I think are more reasonable (for the
   simulated data)

 - small bugfix: since results_df and performance_df have the same index
   in cobmine_first_level_df_with_performance, don't need to pass
   anything else to results_df.join

 - we now catch inf as well as nan losses, and jump to the next
   batch. this *should* allow us to avoid troublesome subsets of the
   data

billbrod/spatial-frequency-preferences,billbrod/spatial-frequency-preferences,billbrod/spatial-frequency-preferences