merge with master
Merge branch 'master' into batch_histogramming

Conflicts:
	datasets/sample_descs.txt
	plots/load_histos2.py
	plots/syst_band.py
	stack_plots.ipynb
using plot defs
added options for symmetrizing errors, disabling stat
removed global state, use NX as backend
use a graphasymmetry
import varnames centrally
use new nx graph
use new tree.py
cleared output
factorised variables, weights and histo descs
fixed wrong class method
cleaned up some deprecated code
batch histogramming implemented
added missing
added missing
Merge branch 'batch_histogramming' of ssh://pata/~joosep/Documents/stpol into batch_histogramming
close output file
Merge branch 'batch_histogramming' of ssh://pata/~joosep/Documents/stpol into batch_histogramming
misplaced sign