[doxyref ] added citations to files from "dumux/material/components"

doc/handbook/dumux-handbook.bib

dumux/material/components/brine.hh

dumux/material/components/brinevarsalinity.hh

dumux/material/components/ch4.hh

dumux/material/components/co2.hh

dumux/material/components/h2.hh

dumux/material/components/h2o.hh

dumux/material/components/mesitylene.hh

dumux/material/components/n2.hh

dumux/material/components/o2.hh

dumux/material/components/simpleco2.hh

dumux/material/components/simpleh2o.hh

dumux/material/components/xylene.hh