GitLab

Also:
* Add composer as facet
* Restructure list view
* Restructure detail view
* Add and improve tests

* change file extension
* remove unused files
* add linting information
* remove obsolete .editorconfig file

WARNING: Preparation patch - merge after go-live!

This change updates the link generation to documentations. With new
documentation server in place, the manuals.json contains more information,
for example the link to the rendered documentation per extension version.

* Change redirect to existing action
* Change text if no version of extension found