Implement twolevel modelbuilding

[gdevenyi]

Twolevel modelbuilding by wrapping modelbuild.sh in another top-level script twolevel.sh

• take in a 2D CSV of inputs
• break into 1D CSVs
• run modelbuild.sh for each 1D with subdirs of output
• reproduce all options from modelbuild.sh
• don't forget to handle single-timepoint subject data properly

Need to either parse every option and re-generate the output, or do something fancy with the entire command line

[gdevenyi]

Can I update dbm.sh to handle this?

[gdevenyi]

Complete after #39