Gitlab-CI improvements

During mingling with the Coverage tests for Krake, I found some parts of the Gitlab CI pipeline that could be improved. More can be added here:

• Activate, zip and store the coverage results as HTML
  Especially useful for people looking to improve coverage or checking, why their MR brought the coverage down.
• Remove doubled pipelines
  Since workflow rules seem to be implemented (here and here), we could maybe now tackle the doubled pipelines, that are running after creating a MR.