Valid input checking for unique indexes

[nehargupta]

We don't check this right now, and it would cause problems if someone inputs a dataframe with nonunique indexes. Add something to data_cleaning.py that checks via: df.index.is_unique

[AngikarGhosal]

This is done

[nehargupta]

Hm I thought that I merged this in but I'm forgetting now and I don't see code that fixes it! I either forgot or it didn't happen or it looks different than I expect...no worries, I will double check later :) So leaving this open for now, I will come back to it.