Stochastic: remove two unused methods
ModelReader: fail immediately if file cannot be found
anim_concentrations: make movies
Remove unused variable and other small cleanups
ResultWriterHDF5, anim_concentrations: write neighbors and graph them

anim_concentrations.py --connections model.h5 | neato -Tsvg > model-conn.svg && firefox model-conn.svg
anim_concentrations: improve edge widths
Write reaction event numbers