Access public resources passing only the client_id parameter

Refactoring in some places to make the code a bit more readable (extension methods, String.Join for array concatenation and some URI manipulations)

Handle now the request to access the public data (only giving the cleintID as mentioned in the API reference http://developers.soundcloud.com/docs/api/reference : https://api.soundcloud.com/tracks?client_id=YOUR_CLIENT_ID)