Automatically create XDF test cases from equivalent open source R test cases.

It should be possible to automate creation of XDF test cases from a test case (list of `inputs` and `config`) created for open source R. The basic logic will be to:
1. Save data frame inputs to appropriately named XDF (admissions -> Extras/Data/admissions.xdf)
2. Update `inputs$XDFInfo` to `list(is_XDF = TRUE, xdf_path = "Extras/Data/admissions.xdf")`
3. Save updated `inputs` and `config` as a test.