Commonalities repository structure

[T-sm]

As proposed for Camara Governance in camaraproject/Governance#47:

We should have 4 subfolders (contributions, working, deliverables, supporting documents) and describe the process in the ProjectStructureAndRoles file:

• All contributions have to be made only in the contributions subfolder
• Work in progress has to be done only in the working subfolder
• If decided by the maintainers that a new release can be published then the files can be moved to the subfolder deliverables
• documents from outside which are needed for the work have to be saved in the supporting documents subfolder

[T-sm]

UPDATE - please note:
Steering Committee voted to use branches instead of different sub directories. New section will be added to ProjectStructureAndRoles.md in Governance's repo with a description how branches shall be used to reflect the status of an artefact.
The Commonalities (and other workgroups) will then follow this guidance.

[T-sm]

Created new branches as requested in the WorkingGroups repo.
Published a draft branching how-to tutorial under the WIP branch.