input/csv: rearrange text to logic data conversion and datafeed

input/csv: rearrange text to logic data conversion and datafeed

Move the helper routines which arrange for the data feed to an earlier
spot, so that references resolve without forward declarations. Rename
routines to reflect that they deal with logic data.

Slightly unobfuscate column text to logic data conversion, and reduce
redundancy. Move sample data preset to a central location.

Rephrase error messages, provide stronger hints as to why the input text
for a conversion was considered invalid.