Implemented Pushout
Merge branch 'master' of momo.mathb.rwth-aachen.de:/home/gutsche/gap/repos.git/CategoriesForHomalg

* 'master' of momo.mathb.rwth-aachen.de:/home/gutsche/gap/repos.git/CategoriesForHomalg:
  Started generalized morphism category.
Several implementations of precompose.