Use suitable header rather than an extern declaration
Fix library categories

fix: "System and Control theory" -> "System and Control Theory"
fix: 'Commutative algebra' -> 'Commutative Algebra'
chg: also corresponding changes to emacs files (although they should better be generated in build time)
sync grammar.y
Merge branch 'spielwiese' of github.com:Singular/Sources into spielwiese
sync grammar.y