Add ability to export single sample calculations to an excel file

[kaylai]

Right now, only batch calculations can be saved out to an excel file. Since the calculate objects contain sample, model_name, and result information, we could allow the user to also export these. This would require the user saved the calculate object to a variable (without .result appended).

Possible solution

We could add a .save (call it what you wish) attribute to calculate classes, which would be a pandas dataframe that contains all of the metadata for that calculation. I think that's all we would need to do, since save_excel looks at the calculations assuming they are pandas data frames and simply passes .to_excel to each.

[kaylai]

Handling multiple cases

Provide if statements for all cases:

1. calculation[i] is type pd.DataFrame (current behavior)
2. calculation[i] is type VESIcal calculate object -> in this case, call .save() attribute that we would create for calculate classes and include any calc metadata in saved file
3. calculation[i] is type np.float64 (any float/int?) -> note that in this case, no calculation metadata will be saved