Add support for scrolling up/down when album list is active

[ghost]

This PR is related to #11

ctrl+d/u should scroll through pages but this has been implemented in "Liked Songs" view only. In this PR, I tried to implement scrolling down/up in the "Albums" view.

need to confirm:
In src/app.rs, I added three methods (get_current_user_saved_albums, get_current_user_saved_albums_next, and get_current_user_saved_albums_previous) for App. These methods are imitation of **saved_tracks** methods. Although push_navigation_stack is called in get_current_user_saved_tracks, I did NOT call push_navigation_stack in get_current_user_saved_albums. If push_navigation_stack is called after each page scrolling, same contents are pushed into the stack. Scrolling pages several time, q key (go back) seems foul-up. This behavior seems a bug for me so I did not call push_navigation_stack in get_current_user_saved_albums.

[Rigellute]

Thanks for taking a crack at this.

I think I've got things into a bit of a mess with regards to pagination (managing page index, scroll, index etc.).

There's a half baked attempt to clean this up, using a more generic struct (see ScrollableResultPages struct in app.rs).

I've got a better understanding of how this should work now and do intend to clean this up.

With regards to your comments, you're right about not pushing to the stack when fetching the next page. Pushing to the stack only needs to happen the first time we want to navigate to that view.

[Rigellute]

Nice one, this looks good 👍