API support for restricting results by scope
See #594: added support for filtering API results (tracks, albums, artists, uploads, playlists, radios, listenings and favorites) by scope, e.g:
GET /api/v1/artists/?scope=me: list all artists available in my libraries
GET /api/v1/albums/?scope=all: list all albums (equivalent to omitting the scope parameter)
scope=me parameter will be used to allow creating a UI to browse personal content, as part of #594. In the future, we me also allow
scope=user@domain for browsing a specific user public content, or
scope=followed to browse content from followed people.
(There is also an unrelated commit to enable MusicBrainz ID filtering on artists/albums/tracks endpoints)