Added Image to universal objects
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:
  Several implementations of precompose.
Implemented AddToGenesis function
SetGenesis -> AddToGenesis
convenience function ImageEmbedding
small modifications in UniversalObjects.gi