Always add OAuth parameters

Tumblr gives you a OAuth key on request. The get the access token, you need to send a fully signed request without the access token. However, this is currently not possible since AFOAuth1Client only adds its OAuth parameters when it has an accessToken assigned.

Also, I've swapped all -setValue:forKey: with -setObject:forKey: because this is faster and the actual idea of this method compared to -setValue:forKey:.

Hope you like it