Merge pull request #37 from steenpass/andreas

update part 1
prepare for elsevier: change documentclass
prepare for elsevier: use yjsco and natbib
prepare for elsevier: remove defn and prop
prepare for elsevier: use frontmatter instead of maketitle
prepare for elsevier: use \ead instead of \email
prepare for elsevier: change keywords command
prepare for elsevier: change title
prepare for elsevier: use environment 'ack'
prepare for elsevier: do not use \boldsymbol