if material units are sum, not value will exist -> value is moved to be read after units
moved copying value before type of unit checked and initialize value to zero
changed fixed source to particle when determining if node particle exists
fixed node pointers to natural elements that were sometimes labeled as nuclides
for plots, <color> is now cell by default (according to users guide)
added empty arg list on subroutines
wrong pointer listed for reading in RGB in <color_spec> node