Something I've asked to be done for a long time. Relevant because I've
complained about this on every addition of a new piece of user-local
state: friends, blocks, and now favourite beatmaps.
It's just so messy managing all this inside `APIAccess` next to
everything else, IMO.
This also fixes code running in `Update` which shouldn't be, by
consuming the new `NewItemsPresented` callback.
Fields and properties are renamed to knock some sense into things (was
previously called two or three different things).
This aims to bring some conformity to naming to make it easier to
understand component structure for new components.
Renames are pulled out of the song select v2 changes and are more
relevant there due to many new classes being added.
- `V2` suffix is dropped, with v2 components being moved to a relevant V2 namespace.
- Related classes have a prefix of the area they are used.
- Experimenting with using partial/nested classes in the song select v2 implementation.
Not committing to this yet but want to see how it plays out.
- Moved base carousel components to a generic namespace to avoid confusion with actual beatmap carousel implementation.