[DOC] Correct ReDoc API documentation

Existing solution based on javascript is not working
- solution based on _downloads reference

Use sphinxcontrib-redoc package
- Update conf.py to add the required extensions
- Update conf.py to add ReDoc API documentation
- Add sphinxcontrib-redoc in requirements-docs.txt
- Remove redoc directory
- Copy Swagger JSON file in swagger repo
- Rename Swagger JSON file
- Correct Swagger JSON file to delete bad characters

Small editorial corrections
- Update doc/architecture.rst

Issue-ID: EXTAPI-599

Signed-off-by: Eric Debeau <eric.debeau@orange.com>
Change-Id: I3c2b52ff072f81f5554046498f0cf8419cc3f342