only load CSV data on demand
only load CSV data on demand

Instead of loading all data at once, load one csv at a time. This
should only use enough memory to load + data per file on each group
which is a much smaller subset of data than all data.

Because the files are processed in conf order, generally VFS cache
will work out nicely between redundant loads, so don't worry about
it for now and KISS

phact/effio,tobert/effio,tobert/effio,phact/effio,phact/effio,tobert/effio