added ACM Categories and Subject Descriptors

using the 1998 caterogies, because it is not clear how to use the
2012 system yet. From the ACM page:
"Tools to help authors apply the 2012 CCS categories and concepts
are being built. A new set of instructions will be issued in early
2013. Until then, authors please continue using the 1998 categories
[...]".
http://www.acm.org/about/class

Also added General Terms, Keywords and Neofonie affiliation.