WIP: Allow for more flexible acro package instead of acronyms

The used acronyms package is a bit limited. For advanced situations (like uncommon plurals or hiding some acronyms from the list of acronyms) the package acro can be used instead. http://ftp.fernuni-hagen.de/ftp-dir/pub/mirrors/www.ctan.org/macros/latex/contrib/acro/acro_en.pdf

This change is definately not pretty and would probably need some additional work (like proper multi-language support)