Merge all DB.nomics projects into one "dbnomics" group

As seen with @thomasbrand this issue is freezed for now.

• As a product owner
• I want to share a unique URL giving access to all the repositories
• in order to ease the discovery of the project.

Proposition

Using the subgroup feature of GitLab.

Place all current DB.nomics groups (/dbnomics-fetchers, /dbnomics-api, etc.) under one unique group git.nomics.world/dbnomics). They will become subgroups which can have their own set of subgroups and projects.

All Widukind projects should also be transfered to one Widukind subgroup under /dbnomics or its own group at the root.

Acceptance criteria

• There MUST be only one "dbnomics" group (dbnomics-fetchers, dbnomics-source-data and dbnomics-json-data are removed)
• Existing projects in the removed groups MUST be moved to the "dbnomics" group

Technical steps

• Update the URLs on the developer machines