ideal solution for source file column indexes

[tarheel]

Proposed long-term fix: UI should scrape column labels and present them in a dropdown for users to choose from

[gngilbert]

I presume we specified columns due to the fact that we started working with the ES&S .xlsx formatted CVRs. As we expend data sources, it might make more sense to specify the source of the CVR first, eg. ESS, CDF, Dominion, Hart... then have the GUI present the relevant options

Since this certification testing is specifically dealing with ESS data, I think we are ok but I like the suggestion for future development.