Adding username and password authentication, failes for some reason and added an ticket at TMDB API http://tmdb.lighthouseapp.com/projects/83077-api/tickets/358-improve-authentication-api#ticket-358-8.

I suspect the api_key has to be ignored from the request as the request matches the earlier discussion in this ticket,
but this would require extra work and actually doesn't make sense as all other authentication requests do require the api_key.
Merge branch 'develop' into feature-username-password-authentication
Complying with the API.
Adding the username and password authentication method for authentication.