Simple authentication

Merge the simple authentication.
It's based on a token that's exchanged in the header of every request.
Login and logout methods are provided and have direct routes (/login and /logout). Login creates a token and returns it and logout removes a token assigned to a user.
Authentication is done through a middleware that verifies the headers for a token with every request. If no token found or token is expired a 401 with an error message is sent.