Add csv output support to NACCulator

[s-emerson]

From Ben Keller at NACC:
And, finally, we have an internal request to change nacculator so that it generates CSV. One of our developers was going to look into this, but maybe someone there could do it faster. This comes from Janene Hubbard who consults with people dealing with the fixed width fields.

NACCulator's default output is in fixed-width .txt format to account for NACC's standard submission format. They have requested that NACCulator have the option to output to .csv format instead. An example of what this output could look like is given in the NACC quarterly data freezes, where each participant has a separate row for each visit event. Right now, REDCap exports use separate columns for the variables in different visit events using prefixes (fu_ for the followup packet and tele_ for the telephone followup packet, for example). The new csv option for NACCulator would essentially remove the prefixes from the REDCap export and combine the "separate" columns for the same variable into one column. So, for example, mocacomp, fu_mocacomp, tele_mocacomp, and tip_mocacomp would all be combined under the "mocacomp" column, with each value belonging in a different row depending on visit number.

[michael-bentz]

Thoughts on how to output to csv

• we need an extensive list of all keys (headers are different for every type of form)
• we can't use records, we can't use a single form or single packet because they don't hold header information
• might be able to reverse engineer set_blanks_to_zero or set_zeros_to_blanks because they contain the logic to apply the correct fixed width