Automatically create pop and demo for CDISC

[andrew-slater]

In lieu of amending the gtx package to handle CDISC data (where the IDSL pop and demo data sets are hard coded), automate the conversion of CDISC to the expected IDSL format (currently expected to be done manually) by allowing a config key pointing to the CDISC AR data set which tableinput.R would recognize and then read the ADSL and ADDM files to write the expected pop.txt and demo.txt files in the input directory