Three changes made here

-- first a rename of plink-qc.nf to qc.nf and plink-assoc.nf to assoc.nf.   The "plink" is unnecessary and
   confusing. We'll keep the plink-qc etc file there via a symbolic link so nothing should break, but in time
   we can phase out
-- When we upgraded our version of Pandas some scripts broke and those were fixed some months ago. However,
   those fixes had the effect of breaking the scripts for people running old versions of Pandas. As some people
   will not want to upgrade pandas because the upgrade may break other scripts, I made changes so that the
   scripts run on different versions of pandas (tested on 22 and 24)
-- minor fix to the nextflow.config file which did not provide the right container for procesesses labelled with
   'latex'