Refactor avatar method and corresponding views to be more concise.

I split up the logic in the avatar method into two separate methods. This makes them smaller and more concise. Instead of deciding the size of an avatar in the view by passing in an argument of 1 or not to the `avatar` method, the developer can just use the corresponding expressive name that is inline with their intent, either: `small_avatar_of` or `large_avatar_of`.