Profile picture helper

[sabuto]

Add a helper to retrieve the profile picture on twitch for the user.

[chris-redbeed]

As I already said I like this idea of small helpers.
I will try to add some, that will handle all the requests and cases to get same information about a user.

[chris-redbeed]

I created a function in the UsersClient where you can get the User data of a user by name or id.
Example:

$client = new UsersClient();
$users = $client->byUsername('movrs');