Legacy to Insight: Pluralize orig_header_row -> orig_header_rows

[ctesta01]

This doesn't necessarily need to be done, it would just be nice style.

When I was originally writing code for Legacy, there was only one extra header row in the CSV data. Therefore, when I stripped it out from the CSV response data, I called it the "original header row" or some variant of that. Now, with "Qualtrics Insights," there are three headerrows and so this pluralization should be reflected in the codebase. However, I think that because I only had to transition from handling a 2xN to 3xN dataframe, and there was no change of data structure in that update, that the problem is mostly aesthetic.