Convert raw spreadsheets to standardized/tidy data

[jsvine]

The current raw data is spread across three Excel files. Each has a main table of individual survey responses, but each with a slightly different set of columns, and a slightly different way of representing the response values.

It'd be great to convert those spreadsheets into a more standardized (and CSV-formatted) dataset, where all respondents and responses are represented in the same way.

In terms of structure: Although we might want to ultimately aim for a more "tidy" approach, I think a good first direction would be to keep the same general principle as the raw spreadsheets: One row per respondent, with columns representing the survey instance (respondent ID, date given, platform) as well as the question responses.

One thing to keep track of: Which data-points are not available in all three spreadsheets? How do we want to represent them (if at all) in the standardized file?