Select global cluster as proteins with >0.5 covariance with the growth rate.
Added analysis of CV of both the protein level and the protein
'weight' for proteins in the global cluster.
Analysis shows weights have lower CV and the difference is ~ the CV of
the global cluster.
Global cluster has much smaller CV than growth rate (0.18
vs. 0.39). plot reveals this is due to global cluster not intersecting
at 0,0. explanation still needed.