Remove g.dart files and let them generate in the CI

As, for example in !198 (merged) lib/Modules/QAndA/Model/category.dart, it sometimes happens that people forget to run the build_runner and thus not generate the needed files for the app to work properly.

So i propose to add another CI stage for filegeneration.

It would take more time to run the CI, but then again we would not need to commit generated files into the repository.