poc adding new code/tests/translations to cookiecutter instance

[zzacharo]

Goal: Prototype how we can add new installable code in the cookiecutter instance

Some initial thoughts:

• [x] Add new folder e.g code or src which invenio-cli installs
  • Minimum setup.cfg file
  • Invenio-cli checks and installs this folder
• [x] Add tests folder which can test your custom code
• [ ] Add a new folder with translations which invenio-cli can copy over

WIP: https://github.com/inveniosoftware/cookiecutter-invenio-rdm/pull/233

[zzacharo]

redundant