Make data use for plotting functions more flexible

[BriVandrey]

Many of the plotting functions rely on reading in dataframes that are assumed to be saved previously in the pipeline:

For example (from PostSorting.make_opto_plots.make_optogenetics_plots)

peristimulus_spikes_path = output_path + '/DataFrames/peristimulus_spikes.pkl'

It would be good if these were more flexible, for example first checking to see if the data exists, and if not, then remaking it or reloading it without saving it. This would be particularly useful in the case of session types like openfield_opto where opto dataframes can be too large to save depending on the RAM of the machine that is being use for analysis. I suggest introducing this feature to the main plotting scripts.