Variety of small changes
Variety of small changes

 - n_classes now gotten by a function, which depends on the mat_type
   and the session (rather than just the session)

 - adds plots_modeling_blanks rule, which creates final plots for the
   summary dataframes for all sessions

 - adds tuning_params.svg plot to plotting rules

 - removes data_dir for preprocess rule's input; we only need to rerun
   if the actual input files have changed and can get get data_dir in
   params

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