Close #94 Enforce authentication by JWT

[EliuX]

In this PR we are requiring authenticated users using JWT. To do so, we are using the library PyJWT, so in every request to the API we expect a header Authorization with a format like

Bearer
In the Swagger UI, you will now see a new button called "Authorize":

when you click it then you will be notified that you must enter the content of the Authorization header, as mentioned before:

Click "Authorize" and then close that dialog. From that moment forward you will not have to do it anymore because the Swagger UI will use that JWT in every call, e.g.

If you want to check out the data (claims) that your JWT contains, you can also use the CLI of PyJWT:

pyjwt decode --no-verify "<JWT>"

Remember that the API is not verifying the authenticity of the JWT, but the API Management.
There is also an additional commit fixing most of our tests in order to adapt to these new requirements.